Yeah, you need to experiment a bit to figure it out:)
Dima, does the Amulet of Valor play a key role? Can the battle be won with a neutral Battle Defender and luck?
Anyway, I'll try to figure out the garrison by tomorrow, and if I have any questions, I'll ask....
Theoretically, the battle can be won without the amulet (but with the Fairy Ring). But a lot of things need to align.;)