I can tell you for a fact there is no formula.

In beta testing I suggested strongly that a formula be used, and even presented a potential one. I’d be glad to repost it here for discussion (if I can find it).

But ET said, basically, that he doesn’t feel it’s necessary. What was done in Ep1 and Ep2 seemed to work, so that’s what he was going to use for Ep3. To change the base would require not only a bunch of coding (which we all know he no longer has time for), and would result in weird balance shifts to everyone who’s been playing for any length of time.