As a result of ongoing ground combat, I've made three changes to the ground combat rules.
1) Ground Combat happens every 8 hours.
2) If ships are assigned to provide ground support or orbital bombardment support and, due to losses, the supported formation no longer has sufficient Forward Fire Direction capability to control all supporting ships, then one or more ships, starting with the smallest, will automatically change to support other formations in the same engagement that do have available FFD capacity. This is to avoid the micromanagement of manually changing support when FFD units are lost. You can still manually override for key decisions.
3) When you design a ground unit class, you can designate it as a 'Non-Combat Class'. A class with this designation suffers an 80% penalty to hit and any hostile unit selecting targets treats this unit as 80% smaller. This could be used for supply vehicles, HQs, FFD units, etc. It is intended to simulate the type of unit that will actively avoid combat and is therefore much less likely to be chosen as a target. This applies regardless of field position.