The best test for the source of occlusion is to turn the aid off and place it in the ear: then speak.
If your voice is still booming, physical modification to the venting is needed.
If the booming only happens only when the aid is turned on, try altering the 500Hz gain in both directions to see if this reduces or balances the resonance. Sometimes more gain here is beneficial if it is out of phase with your voice signal.