I'm unsure what the cost increase formula for incorporating is, but I think you figured it out before including the increase in earnable PB? This may not be a problem, but it occurs to me there's a non zero chance that a players entire run might be difficulty adjusted for "number of corp completions" rather than "prestige bonus strength" now that the two are not hand in hand aligned. That'd massively, permanently favor players who went deep instead of wide on their tech breakthrough choices.
Just a thought. I can't see the math on this end (at least, not without about a year of playing and recording variations!) so I'm not sure if it's a real concern or not.