Gremlin power

[Xargon]

Another question which is probably known to veterans from the previous games:
How is the power of gremlin towers calculated? Previously, I thought that it is mainly determined by the item, but then I experienced something strange: Over time, I had a couple of suppression battles with the archmage's staff, and the first few times, the towers had by far the most powerful spells of any item battle so far: their lightning bolts dealt 2k damage to the primary targets, retaliation dealt 600-700 damage to Royal Griffins (30% or 40% magic resistance, I think), etc. They had only about 3500 health, though. But the last time I suppressed the staff, their spell power was ridiculously low, while everything else (health, troop numbers) was unchanged.