I don't think reverse tolerance is a thing, truthfully. I've written extensively about this before, so I'll summarize my previous thoughts.
Most people don't know how to properly prepare kava, including how much root to use, how much water to use, methods of extraction (which is why I include specific instructions on each bag), and proper equipment (which is why I include a free 80 micron strainer with each order). Many folks end up drinking one shells worth, thinking it'll hit them like a brick, but they don't realize the really obvious effects normally come on after ~2-3 properly prepared shells. They're being responsible by not drinking too much on their first time, but it's generally just not enough.
Once you've been drinking it a while though, you can generally tell how strong a batch is by your first shell and the first signs of being rooted.