How many troops form a "large enough" force?

[Amhazair]

ano said:
Just checked it. Pythium gets Leo at defense 20.
Seems like mages in enemy force cause executing of gem-demanding scripts.

Good catch, and this might very well have something to do with it. It's definitely not the only consideration though.

I have on a couple of occasions used a couple of castings of ghost riders against large opposition armies for the sole purpose of having them use up their gems. Two castings is definitely enough to force gem usage, I haven't yet tried it with only one. Ghost riders don't have any mages, but they do come with a rather scary thug leader.