You might also like to consider the similarity of steps 4-6 of the reverse wave as lady

well the lady's for 4-6 of the wave are exactly the same as the mans steps for the three step - so the same questions would arise. i'm not sure if the comparison illuminates the situation further - except to say that this pattern does gives the very abrupt rise of fall ie the wave effect - which come to think of it, is something i like, and accept as a feature of that figure. perhaps the intention was to have that same effect on the three step although if that were the case i wonder why they didnt call it the forward wave.

Interested. Well i'll be darned. I never realized before that if i follow the book as it is written i could do a Feather Step followed by a Feather Step and keep going untill the music stopped.
Hot Stepper. Just accept it. The only other way would be to go back in time to the 20's and ask. There is probably an answer. Remember their was a Three Step before there was a Feather Step. The Feather was a cross up behind untill about 1922. A Reverse Turn didn't have a Heel Turn . It was a Viennese Cross. Information from Victor Silvester's Modern Ballroom Dancing. which is probably in your local library

I think the original post should ignore the advice of Cyd to just accept it .

Understanding the thinking behind technical details often turns out to be important when it comes to adapting figures and working out which features are intrinsic and which need to be modified. Even if a definitive answer does not emerge there is usually something to be learned along the way.

To put it another way .... as scrivener pointed out.. no technique can be exact as circumstance may change the theory ( para phrased )

A quote from Victor Silvester - "Theory and Technique of Ballroom Dancing", 1936, in example questions and answers:

"Q: Why does the rise in the Feather Step differ from the rise in the three-step?

A: Because you step outside your partner and therefore it is more natural to rise one step earlier."

Well at least there is hint of an answer there, although I dont know why rise shoud be more natural when going OP.

The "rise " O.P. in essence is absorbed by the extension that needs to be created thru that "position".

A common tendency for the man, is to step short ( R foot ) when moving out side partner, causing an upward "swing" thus impeding the Fwd action