I have a suggestion about ground force HQ and fire direction units:
Make them have another parameter - operating range.
The simple explanation is: have options for HQ and fire direction units to be:
Planetary - which essentially limits their capability to command/direct fire the units in the same planet and it's orbit, Generally, what we have now;
Solar System/interplanetary - Allows commanders in HQs to provide bonuses to units under their command while in the same solar system, and FFDs to provide coordinates for ships/STOs further away from the planet;
Sector/Interstellar - A bit like Naval Admin command range, it is generally relevant to the HQ formations than FFDs (since, I don't know if you can fire a missile, make it go through a wormhole, and then find the FFD's indicated coordinates?)
This feature would allow to design 'Command and Control ships', that can hold, like, Army group HQ (rank 7, with like 1. 000. 000 Command points and Solar System/Interplanetary upgrade) that provides commander bonuses to units fighting on a Planet in this system (with just planetary upgrade), while this Army group HQ could itself be attached to a 'Earth High Command' (rank 8, with 10. 000. 000 Command points and Sector/Interstellar upgrade).
For FFD unit, with Solar System/Interplanetary upgrade, it could direct fire from a STO on a moon that is orbiting the planet on which the FFD is.
Mechanically wise, these options can function similarly to upgrades that we have now. What they essentially do - in case of HQ unit, they double the price of the HQ unit if it is Solar system/Interplanetary upgrade, triple or quadruple (perhaps there can be another variable, like with Naval Command HQs), determining how big their operating range is.
Generally, another mechanically supported role-play option. It would allow us to have a more interesting means to disperse our forces across solar systems, making dugouts and small defensible fortresses on them a more viable strategy in terms of defending the solar system.
Semi-autonomous bases on asteroids further away - Activate!