With a strong grip cupping the lead wrist at the top can put the clubface in the proper square to the plane position. keeping the wrist flat will put the clubface in a square to the path position or shut by normal teaching criteria.
There is nothing wrong with cupping the lead wrist at the top and a lot of great players have done it. The wrist can also be cupped at impact and still achieve the y position that is critical for good ball striking.
IMHO if you want to use a swing that demands a flat wrist at the top with clubface in a square to the plane position then you don't want to use a strong grip. I believe that is exactly what you have figured out? I know that Scott Hazledine and Todd Graves both recommend against a too strong lead hand grip.
As for gripping it really tight I am experimenting with that idea. So far it seems to be helping me in that I am able to overcome my tendency under pressure to tighten up on the downswing. I guess that for me a really firm grip mitigates against the hit impulse...
