I would've answered that I drink until I peak, but a real peak has become so rare to me it wouldn't be the most fitting answer. I can say though, that when I have a had full peaks, I am completely satisfied afterward and feel no need to continue drinking.
I've learned over the years, especially since kava strength has gone down (and/or my body has started to react differently to it), I will just drink a predetermined amount every night. I spent a year or two raising my dosage and drinking more to see if I could bring on the 'full experience' (undeniable peak) again that way, but it typically didn't work and often would lead to nausea or difficult next-days plus worse dermo. Around the same time, kava prices started shooting up, so it just became wasteful to drink extra and still not get the ideal experience.
The first 3 answers have been true for me at one time or another, but the one that holds true for me now is
drinking a predetermined amount, if that amount doesn't hit hard...it's pointless going beyond it cause it generally hits a point of diminishing returns.