I didn't experience reverse tolerance myself, that I was aware of. My opinion: I think that over time I learned how to enjoy Kava more and so it is just better now than when I first started drinking it. Maybe this is reverse tolerance, but I think it is a combination of things: How to make it properly, when to drink it, how much to drink, what kind to drink, what to do after you drink it, etc. Lots of little things that when all combined together make the kava experience more enjoyable.
There are some really smart guys on here who can give a response to this based on real facts, so hopefully they will weigh in.