variance on sims?

[Lorthania]

This is probably just me, but why is it that sometimes, my cabby alt casts a pet that can just about do a yellow con and then the next time, he gets a pet that seems to have no problems with orange cons? The mob is the same type, so it can't be resistance to a certain damage type.

So, is there some sort of variance on pet casting and/or the buffs you place on that pet or should I just stay out of the heat for a while?

Grtz,