All right... Like a politician dealing with competing constituencies, I've tried to fashion a compromise. The "No More Bionic Squares" rule is now part of the Optional Rules PDF.
The "Bionic Squares" thing is an easy rule to write. I think that's done.
As for the other point about whether or not you can use the Reaction Phase to change formation in a tricky way that will halve your attacker... I just can't find a way to write that, to make it clean or to avoid unwanted consequences elsewhere.
I stopped short of Cam's suggestion. To review: Cam had suggested that if an attacker charges you in such a way that he gets his full dice because you're mostly to his front when he charged... then no matter what you do in the Reaction Phase, he'll still get his full dice. (Thus there's no incentive for the defender to try a tricky formation shift out of harm's way.)
But I had some issues trying to write it, as well as some fundamental second thoughts about the whole situation:
1. I can just as easily see a rule like that being abused by an attacker, to squeeze more attacking units in at funny angles... instead of doing what he's supposed to do, which is to try to hit the defender head-on, thus contacting multiple defending bases, and/or contacting the defender in more or less the middle of his formation, making it impossible for the defender to slip out of the way in any event.
2. I was worried that it would make cavalry too rigid. In the case of cavalry I definitely DO want the defender to be able to slip and slide around, with a bit of luck and good deployment, to avoid an attacker's full onslaught.
3. I'm generally averse to any rule that asks people to go backward in time and remember a situation that no longer exists on the table. (i.e., "Yes, I realize that you're over there now, but when I charged, you were over here, and thus....")