Should we also be removing the inflation offset variable at the same time (I'm not sure what that does either)?
Edit: upon testing. Based on my calculations, this is what appears to be happening: upkeep costs are running after unit costs are adjusted, but the tooltip is (somehow) displaying at default levels. Rifles are costing 28
upkeep on marathon speed, which is precisely what they would cost if they were 3x cost and everything else held stable. Inflation either isn't a factor. Or if it is, it's not significant. It's displaying (if you take out the gamespeed adjustment) at 13.
Buildings appeared to be impacted slightly such that costs were predictable. Building upkeep is set however independently of cost, so if inflation is acting upon it, the change is standard across game speeds and ultimately minimal as nothing costs very much
to start with.
Unit upkeep changes based on game speeds because unit costs go up or down (and could be then impacted by inflation). If upkeep calculations are running after game speed affects things, that could explain why a later game unit is roughly 2x cost in marathon as about half of the upkeep formula is cost based. It would not be 3x as unit upkeep is significantly influenced by unit strength, which is fixed. This would also be why earlier game units are not as noticeable as there's not as much difference in the cost function for a scout (120) or warrior (140), versus a rifle (800) on which to act.
It's not obviously clear why the tooltip isn't automatically updating to reflect the game speed cost adjustment, but the adjusted formula for display was itself incorrect. I'm not liking the idea of setting the upkeep manually if there is not some kind of automatic way to adjust this. I have so far been unable to make the formula respect the game speed and display an accurate total on my end.