My interpretation is along the mystical "listening to the kava" vein of thought. I have had experiences where kava has not affected me much. When I first started trying kava, it seemed to take a few sessions before I knew what to listen for. I've read other posts that use this explanation for reverse tolerance.
There have been other times though, where I'd been drinking large amounts of kava several times a day for weeks, and it wasn't quite there for me.
I think it is somewhat psychological. When I get into a routine of drinking kava at every available opportunity, there comes a point where I'm not seeking anything of introspective value. I'm just mindlessly indulging. Kava is truly unique and satisfying every time I drink it and im in the mindset to listen.
When I take a jug along with me to the loud, belligerent house party (and I AM that guy quite routinely) I don't get the same, powerful response as I do when I'm at home or out in the park, and in a mood to think....deliberately.
I am rather thin and I have a generally low tolerance for alcohol and other drugs, so it could be that my physiology allows me to not notice my tolerance or lack of.