Spells vs EnemyFollow

I just had a few questions that have been nagging me about my spell hits on some enemies (PvP and PvE)
Although it doesn't seem to happen in PvE as drastically, I noticed that sometimes my spells aren't doing the damage they say they should, so I was wondering what is factoring into my hits.

One example (PvE) was in Strand of the Ancient BG, another guy and I were taking down a horde warrior and my holyshock hit him for 808 damage. My spellpower is around 1400 and the holy shock spells says it does like a minimum of 1296. I thought it might have been just a fluke but when he was low and I threw my hammer of wrath at him, it only did 707 damage. Example 2 is in PvE, when my holyshock is underdamaged again (not nearly as much as the player hit), but it still doesn't do the damage it says it should be doing.
I thought maybe they had some high defense, but defense said it only blocks against physical attacks(damage), I then thought maybe resiliance, but that just lowers the critical chance against them. I thought then maybe it was because of their lvl (80), but then I thought why would a spell(upgrade) that I got at lvl 80, not give the damage done to something at the same lvl?
So I bring it to you guys. Why would holy shock spell that should deal 1296 base minimum dmg, + my 1400 spell power, only do 800 dmg? I couldn't find any formula's that calculat holy shock dmg, so should I be doing like 1696 minimum dmg?

Damn warriors with their shield walls and make-out parties....
Thanks! The math sounds a bit better now, thought I couldn't find a calculator for HS damage.