Quote Originally Posted by Come in Nighthawk
AI has no problem exceeding 20 units in a "stack," but "I" can not [THAT is a separate but related question, BTW]
No it cant, it just look like it. Its hard to explain.. but on the campain map, if you double click a enemy army, a 20 unit stack will look like this:

00000000
00000000
00

each "zero" representing a unit card. If you look quickly it looks like 22 units, but if you count its only 20! Hope that made sense!