Here's one for the crew. On a forward step after the heel lead the man lower the toe to the foor imediately.
The lady at the extension of her stride will only lower when her moving foot is level with it.
Why is there a delay. Simple the man bends his knee after arriving on the supporting foot forward.
The lady also bends the knee forward, which is in the opposite direction to the man.
The reason for this is because the knee can only bend one way and that is forward.
I met a person, a male who having memorised the man's steps didn't bother to look at the ladies steps. Thinking they must be a mirror image of each other he was teaching the lady to drop the heel on arrival.
That sounds like somebody else I know.
To clarify things. The man lowers the toe to the floor imediately.
The lady does not lower her heel to the floor untill the moving foot arrives under her body..
If it is done any other way the ladies weight will pull away from her partner.

"Here's one for the crew. On a forward step after the heel lead the man lower the toe to the foor imediately.
The lady at the extension of her stride will only lower when her moving foot is level with it."

Actually, if you look carefully you will find that they come very close to lowering together.

"Simple the man bends his knee after arriving on the supporting foot forward.
The lady also bends the knee forward, which is in the opposite direction to the man."

Not really, because the lady is also turning her standing leg, which means that her knee is no longer moving in a direction opposing the man's, but is at least halfway to matching his direction.

"The reason for this is because the knee can only bend one way and that is forward."

Yes, but what direction "forward" is happens to be in the process of changing during that time - somewhat by the turned in placement of the foot, then continued as the weight rolls across the foot to the inside edge.

"The lady does not lower her heel to the floor untill the moving foot arrives under her body.."

No, she must do it when her body arrives on the foot.

"If it is done any other way the ladies weight will pull away from her partner."

Not really, because the body weight is almost over the foot already by the time the foot is actually placed. If they've really sent the body into the step and aimed through it, the necessary motion is going to be full enough that it's going to be pretty hard for her to fall ahead of it by neglecting to resist with her arriving leg. She could still of course ruin it by letter her upper body go over backwards, but that's a poise problem, not a foot action one.

But the problem you describe IS much more likely to be an issue on step 1 or step 4 type actions following a foot closure lowering though, because precious few couples manage to actually project their bodies fully into such a step. On step four of a natural turn or spin turn, it would be very easy for the man to collapse too early into his heel because the lady probably will not manage to project her body into a very full movement, so he can easily outmove her. In contast, starting with a nice full passing prep step, it's easy enough to create such a full body movement that it would be really hard to fall onto the heel too fast.

I wrote.
The lady does not lower the heel to the floor untill the moving foot arrives under the body.
You wrote.
No. She must do it when her body arrives on the foot.
So whats new. Where is the difference
This is where you really have got it wrong when you wrote.
Not really because the body weight is almost over the foot by the time the foot is actually placed. That my friend is lowering prematurely. Which is in direct contradiction to the first sentance, which I copied straight from the technique book.
As I have suggested before. Go and look for yourselves. This is a Backward Walk we are discussing, which can be followed by as many as you wish whilst practising solo just to get the right action which you will take with you when you are in a partnered situation.

This concept of 'immediately' is an interesting one. I don't believe in immediately. There is some time between the man planting the heel and the foot becoming flat. Nothing should be sudden (except possibly in tango) as this is bound to give a jerkiness. Moving backwards for the man and lady is different. If the heel were planted 'immediately' it would change the angle of the leg and also change the leg action. Not to mention jerkiness

Phil. The best advice I ever had was to take the shoes off. And to use the whole of both foot from the heel to the toe and the toe to the heel by rolling them to their position. Both feet working. Myself I very often dance in stocking feet since I was told the above. If you have a tape. Take a look at the incredible height of the heel off the floor by the lady or the person going backwards. I used the word incredible because the lady is up to three inches off the floor at the start and still they get more. That's the top dancers of course. The rest of us can but try. Keep Rolling.
I will add John Wood's advice
He says. Two beats for a slow is slit into four half beats. Three are used on the actuall step and one half with the moving foot coming under the body. There it is from a master. The book does say on the walk forward lower immediately.

"This is a Backward Walk we are discussing"

That is your FATAL ERROR!!!

The first step of a natural turn is a member of the family of backwards actions, and a cousin to the BACKWARDS WALK described in the textbook, but it is NOT the literal BACKWARDS WALK described in the book.

Try to dance it literally with all the details of the BACKWARDS WALK and you will fail - because you are then dancing a DIFFERENT ACTION.

This is an intersting one if you go into it. A lot depends on the way you have been taught. At the end of the step the toe is lowered and the moving foot will come under the body. If this is a Natural I will turn over my right foot and my moving leg will still come under the body. It doesn't matter if this is straight or with a turn the moving foot will come under the body. This is called either a neutral position or by some a balance point.
This gives us the same action for all simular steps. Why should they be different. Why should we have two ways of doing a Forward Walk
And to go with John Wood if this is 4/4 tempo. We split the slow , two beats into four half beats. Three we use on the step forward. the remaining half beat is the neutral position.
If this is 3/4 tempo we call the first step 1 and.. If this is a series of Change Steps down the floor we still come into a neutral position before stepping to the side.
All of the above is a Forward Walk of course.
On a Backward Walk we still have a neutral position or balance point to either turn and step to the side or keep on going. We wont go into NFR here, but it is still part of the package.