Also, from a penalty standpoint, there’s no reason for Russia not to declare war on Japan on R1. Declaring war doesn’t require them to make an actual attack, but it does open their territories up for friendly occupation, making it that much more obnoxious as a US bomber base.
By the way, this sealion airstrike scenario is also the reason why Britain starts out with a mech. It can go to Eireland and back to London in time for the invasion.