Per the IRC a vent stack is required to go 6 inches above the flood rim before it goes horizontal. Per the IRC and the " Studor" brand specs an AAV is only required to be 4 inches above the the top of the trap arm/fixture drain. Now the UPC say (local) on AAV specs. So your area may be above as you state but here in Texas we use the IRC. I agree that I would only use an AAV if it is extremely difficult to do a vent stack. I would also only use a Studor brand AAV.