Put into the context of the open reverse vs. the heel turn reverse: The second step is the moment where the two of you will be drawing that circle, the moment when you will either be dancing around the lady while she remains on one spot, as in the heel turn, or the two of you will be stepping sideways around two concentric circles, as in the open reverse. But the distinction between the two types of turn actually begins quite a bit earlier than that, after the first step has been placed. It is at this moment that the timing of your progression to your rotation is crucial. If your progression is too dominant, especially that of your left side, you will force the lady to progress beyond her first step, and she won't be able to close her feet even if she tries to. This, of course, is exactly what you want to do when leading an open reverse: You want to cause her to move off of her first step and take a side step with you. But in the case of a heel turn, you must moderate the progression of your left side, and once she's on her foot, divert the direction slightly so that your left side moves around her, so as not to disturb her balance over her foot as she turns.
Again, this all comes back to understanding what you're trying to ask your partner to do: When you want her to balance over one foot, you'd better not push or pull her off of that foot. Everything at that point must be done in service of keeping her balanced on her foot, and when you approach it from that perspective, you will be more successful at moving your body in a way that maintains that balance.
To that end, I will suggest one last exercise. Starting in a wide closed facing position, lead the first three steps of a reverse turn. Do this several times in a row, choosing at random whether to lead the heel turn or the open reverse. Each time, after you have placed your first step, pause momentarily, taking the time to think about whether you intend to keep her on one spot, or move her off of her foot as you move off of your first step and into your second. If you are consistently successful, you can gradually over time shorten the distance between you and your partner, with the goal of eventually executing it in body contact. Just remember that decreased proximity = increased difficulty, so take your time working toward that goal. And if your success rate decreases too much, you must dial back the difficulty by increasing the distance to one you can handle.
You may also hear others recommend using a slightly earlier rise to assist in leading the heel turn. This can also help for a number of reasons, and should not be overlooked ultimately. But before you go pursuing yet another skill, start with the above exercises, simply for the purpose of teaching yourself the core principles of the timing of your rotation. You can always conquer more beasts after you've slain this one, or at least given it a good, solid beating.
I hope that helps. Good luck, and happy dancing!
Regards,
Jonathan Atkinson
www.ballroomdancers.com