Thanks for the feedback.
I think it's just going to come down to the particular story, for me. I'm not going to force scenes to fit a particular installment size; what I'm doing is figuring out what feels right in the first part of the story, based on the complexity and planned length of the story. Then I look for break points, whether they're natural scene breaks or cliffhangers, revelations, etc. that come at approximately regular intervals.
I can't see going under 500 or hitting 2000 very often, but within that range my stories are all over the place.