yeah you probably have to target an enemy squad because it only affects them when they are hit i think .
i have not used these spells so far though because i think they are not worth it :
what is your e2w1 caster ? a standard van dwarf with lucky water pick ? a pangenean lucky pan with water pick ?
your god ?
the problem is iirc it works only on normal armors not magic ones ( = forged ones ) . so against scs it should not work and against knights etc. in general air / fire battle magic is better anyways .
i guess you are playing vanheim or pangenea .
if you are vanheim you should imho use air battle magic instead ( lighnings , orb lightning , false horrors , ghost wolves etc. ) and as pan earth + naturemagic , e.g. blade winds etc.
normally use air / fire as battlemagic and earth as forging / summon magic

at least i see earth as this personally
weapons of sharpness or petrify are nice expeptions of course