MA Ulm - you called me a forge what?

[BesucherXia]

A somewhat related topic: I just met some problems using Magma eruption.

I had an army of round 60 regular units(hold and attack), leaded by serveal master smiths.
All smiths were scripted with Summon Earth Power - 4x magma eruption. But when they met a single SC (mistform - mirror image - attack close using winged shoes) on the battlefield, all of them refused to use that spell. They even perfered a melee attack with the enemy, which made that battle simply a total slaughter.

What's wrong with them? The SC has 50% fire resistant and 20 protection. Should that be the reason for my smiths to change their mind? Any comments will be sincerely appreciated.