I have the Necromage perk, and have no spell absorption effects, but I can't get Circle of Protection to even turn simple draugr...any reason for this?

It seems to sometimes work and sometimes not, mostly not for whatever reason. This spell should be one of the best Turn Undead spells, but if it doesn't even turn restless draugr, what's the point?

Tried dual casting it?

It will cause undead up to level 20 to flee. It is an expert spell. The best one is the master one, Guardian Circle, which sends level 35 undead fleeing. You could also try casting both. Do the Circle of Protection and then right away cast the Guardian Circle.