Hello all,

One of my players is playing as a Shifter Druid with the shapeshifting alternate class feature and I am writing a couple of effects to make this work:

Predator Form - STR:4 enhancement;AC:-2 armor; AC:-1 shield;AC:4 natural; Predator
Beasthide Elite - CON:2; AC: 4 natural; IF:CUSTOM(Predator); AC:8 natural

These work as intended. The negative ACs are to represent the character's equipment melding into him and becoming non-functional. The issue comes when I want to use an effect to represent Mage Armor being cast on him.
When I try this:

Mage Armor - AC:4 armor

this is where things go off the rails. What it currently does is cancel out the -2 from Predator Form but does not add the difference to his overall AC. I know that I could just type it differently, but that can cause issues if I have to attack him via touch or flat-footed.

Am I coding this incorrectly?