I hear what you say about naps being all over the place. Makes it REALLY hard to follow EASY.
Not an expert, but the first thing I would suggest to work on is increasing the length of those shortish naps. Has he always been a "short napper" or is this something relatively new? Adding A time usually gets them to increase nap length, provided they're not already OT, which does'nt sound like this is the case.
My lo is 7.5 mo is now doing 3hrs A and is sleeping for 2hrs +, so I normally have to wake her (I love having to wake her as opposed to her waking early from a nap).
I agree with mmom, as A's get longer (and naps), he'll drop the catnap more easily.
HTH
Nadene