So for example, if you increase Japan’s economy by 10, Germany by 12 and Italy by 6, that’s a total of 28. You should therefore increase the Allies’ economy by 28 as well, not by 42 as you’re currently proposing.
Actually the Allies’ increase is 32, not 42. USA +13, Russia +9, UK +10. So the Allies would make 4 more IPC’s than the Axis. With more money floating around, 4 IPC’s shouldn’t make much difference. That could be easily adjusted in setup.