My air hole is rather large

,I can't say accurately what size cause I used a file to open it up. I too have been getting maybe two days at best with a given wick/coil setup before things start to taste nasty.
I asked about this a little while back and didn't get many responses, but perhaps your theory is correct. I have to think it has a lot to do with the type of juice your using as well. Mine are all pretty sweet. My peppermint ice cream is a dark amber, and also the worst offender when it comes to longevity. I've gone to changing that wick every day. My best performer is a simple mixture of VG, EM and peppermint oil. It is sweet, but completely clear and at times has yielded up to fours days out of a given wick.
I have been getting better performance over all with a larger coil and loose cotton for wicking. I now make my coils by wrapping the wire around two q-tip stems and I end up with an oval shaped coil. I orient it so that the long side of the coil is sitting vertical. It looks like an old radiator sitting on the ERA. This allows me to get more coil area in the atty without touching the top cap. I then loosely stuff this with pure cotton. Its not densely packed, but fluffy enough to just touch most of the coil. When wet this material swells up filling up the coil area.
That's my set-up du-jour, who knows what will happen next week...