Here is a screenshot of the enemies base right before I destroyed their commander. Had the odd few air attacks on my base during the game, but nothing major. But if he would have just attacked me with the units he had, he probably would have won. (Note, most of my base was on water / island)
This was a skirmish. AI was on normal. 1.0. I've seen the ground unit clumping before, it's almost like they can't spread because of the mass numbers of units. The base was also surprisingly small, considering the game length.