Because it is like asking, 'how long is a piece of string'. There are too many variables to give a proper answer. Things like temperature, type of buds, RH of buds, etc (I only use mine on a wpa at max temp flower mode and would get half the amount of hits per bowl than you do)I've searched this thread for an answer to this question with no joy
At least there is now a starting point if anybody else does a search.