You're probably mistaken, as acceleration without Air gives +3 (100%) with the basic Air skill (I don't remember) and +6 with the advanced one, and +6 on all with the expert skill.
You were probably standing on "your" territory... or maybe something else.
Added 2 minutes later
They cast it without mana, but only 3 times per battle.
And this isn't magic, but their ability, just like with the tent - it's all an ability. Trolls also regenerate not with magic, but with an ability.
