Question about ranger AoE
 

My 22 ranger now and then has occasion to use his little lightning-based AoE, which does 25 dmg per mob and is only rarely resisted by any mob.

I have noticed though that the spell also targets the guy who cast it. Sometimes I get a successful resist but sometimes not. Also I notice that unlike the mobs, on whom the damage when it lands is always the full amount, on the caster the damage taken ranges from 5 to 25.

Is that how AoEs are supposed to work, the character casting the spell also gets hit with it? Or does the above mean I am doing something wrong in how I deploy that spell?

Invoke Lightning? Just target your mob and make sure to have a little distance between you and the mobs. You only get hit by your AE if you're within distance of the group being nuked.

It's a 4 target aoe spell. So if you are in range of the target casted on you will be one of the 4 max targets hit. Many times these are used at range during quad kiting. The damage range is because your resist calculates into the dmg. So sometimes you will resist full and others it will be partial damage.