[B0rsuk]

Here's a hint from inexperienced Dominions player: you can mix various units in same squad. So you can mix both BIG and little units in same squad. This should more less average the size of your units, making them indirectly less vulnerable to area effect spells like Banish. Essentially, it should make your little units effectively occupy more space.

Not tested.

By the way: there should be a formation option allowing you to affect spacing/spread of units, so you can simply order little units to loose formation, sacrificing gang-up potential for improved AoE resistance. Would add yet another tactical layer to the game, I can't see how it could harm the game.