I agree that assaulting into mines is a little unrealistic since you are immune to the mines, but at least in that case the other player had to put his troops in the mined hex in the first place to be assaulted (it being very rare, if even possible, that units retreat from direct fire
into a minefield). That is one of the reasons why I wouldn't generally, as the defender, place my units in mined hex, since I am just negating my own mines.
In the event of an attacker moving into a minefield, getting disrupted, and then the defender counter-attacking into the mined hex, it makes some sense that they wouldn't be affected by the mines since they probably know where the mines are placed. It could be considered that the field was likely even designed with attack lanes through the mines that the fielding side could use if desired.
On your second point, it is definitely not gamey to shoot a tank in the back after a retreat. If I am lucky enought to get a retreat on an enemy tank unit, what am I supposed to do, leave him alone because it isn't fair to shoot them in the back?
That is merely a side effect of using the
optional armor facing rule as it is currently implemented. If you don't like the side effect, don't use the rule. Just like the extreme assault rule, right?
Or if you're on the Matrix team, you can just redesign the rule.
I don't typically have that much problem with wasting any prep since I typically perform my direct fire preparation
before I set up the assaulting units. So I don't generally have the chance to retreat units after others are committed. On the rare occasions where I have retreated the defender out of a hex, I just cancel the assault and move on. It's probably why I never had the crash before.
So, I still consider it to be mostly gamey to circumvent op fire with a assault on noone. I'll admit, less so if it was a happy coincidence, but definitely in my mind if it is done intentionally with the hope that you can get the retreat and move into the hex for without op fire. The only redeeming factor would be that you still have to pay the extra 20 APs to assault I suppose. It could get really bad if you used this "technique" with a banzai attack though.