Define your mega stack.
Sorry, just saw your reply now. I guess the answer to that is a subjective one, but for me, 4 or more units per stack starts to become almost unplayable (also depending on unit size of course). There's too much going on and a sense of just throwing everything in there and seeing what happens. On a 3 front attack you might have 18 or 19 units participating!
I have no problem with the unit scale, but perhaps a different map scale might avoid over-stacking? As I mentioned in my earlier post, the Tiller Panzer Campaign series has a similar scale but I get the feeling that hex sizes are smaller? Which perhaps allows you to fit more units in a given area without overstacking issues.

