There is also the question of how orbital to surface combat is handled. If TN beam weapons function normally in a gravity well then perhaps the current restrictions on beam weapons in atmosphere are removed, or lessened, and the combat becomes between PDCs and orbital warships, with the PDCs benefiting from better armour and perhaps more powerful beam weapons. If that is true, then there needs to be some reason that orbital warships can't simply wipe out ground forces.
Well logically space based forces should be able to wipe out unsupported ground based forces easily anyway. Even if you don't have lasers to burn down through the atmo you can just drop kinetic strikes using rocks, debris and especially dense Ensigns. The problem with kinetics would be that even if you're using relatively small, hardened KSVs they're going to do some serious collateral, and of course if launched far enough away ground based scanners would likely be able to detect and vector said relatively slow (at least in a TN military environment) projectiles and feed that data to ground based defensive lasers to shoot down. Now lasers are preferable because they're precise, and require very little in the way of resupply.
That said space based lasers run into problems against ground based due to the fact that a ship based power supply is always going to limit, to a certain extent, how much actual damage the laser can do through the atmosphere. Whereas groundbased lasers can draw from entire planetary power grids and thus can afford to be both large enough and powerful enough to punch up through the atmosphere and out into low orbit. Not to mention planets are generally speaking wonderful natural heat sinks for the operation of lasers compared to the finite heat sinks available to ships.
Though the big advantage a ship based laser will always retain over one based in a PDC is that it can always dodge. A PDC is stationary, and once its fired it's not exactly going to be difficult to find and obliterate with concentrated fire, or even by pulling the ships further out and throwing some rocks down the gravity well. Leading to some interesting strategic decisions, do you have lots of small PDCs that mount a few lasers and sufficient armour to survive a one on one engagement with an enemy ship, thus allowing you to activate them slowly in order to wear the enemy fleet down whilst retaining a few hidden points to use when the enemy finally brings the troop transports close enough to be vulnerable. But at the same time risk those same small PDCs being easily found and overrun by enemy ground forces if they are willing to land troops in the teeth of a determined ground based laser grid. Or do you build massively armoured PDCs with multiple huge lasers capable of knocking out enemy ships, shrugging off hits, and resisting ground based attack at the same time.
Past that you could also add an army unit type, mobile surface to orbit lasers, basically mobile ship killing lasers whose entire purpose is to shoot and scoot as much as possible, granting ground based forces some measure of anti-space weaponry without having to build and ship PDCs. Useful for either strengthening a worlds defences (or even as a stopgap defence before PDCs can be built), or to accompany invasion forces in order to provide some backup against enemy airpower and potentially even space forces in case the invading force manages to lose control of orbital space.
At the moment, I believe, units can stay hidden in PDCs before heading out and engaging enemy units and thus revealing themselves. It might also be an idea to potentially give units a limited ability to just naturally hide, representing the fact that any space based military would recognise that modern surface units need to be able to hide themselves from orbital forces in case they lose control of orbit to prevent those units being vaporized in short order. With perhaps a small chance every day or so that a unit will be discovered, in part or full and thus open itself to orbital fire and so lose some strength and cohesion. You could even add the option for ground forces to attempt to fade into the background and attempt to carry out a low intensity war, using small units to prevent orbital strikes taking out to many of them in one go whilst continuing the war until hopefully the navy turns up to turn the tables on an invader.
All of which would make for quite an interesting way of approaching conflict in the game. The ability to heavily fortify planets with hidden surface installations would make planetary invasions a lot more chancy, with the risk of lost or heavily damaged ships much more likely. Far more so than now, where a force capable of wiping out orbital stations and driving off the enemy defensive fleet is much more easily able to assume complete control and if necessary lob TN missiles down the gravity well to quash the obvious resistance before landing troops. Instead invasions could become a little like sieges, with space based forces probing the ground based defences, seeking to tempt the defenders into revealing a few PDCs here and there in order to knock them out before guaging when to launch the invasion, all the while hoping the defenders didn't hold back too many PDCs or Ground to Orbit laser brigades to make a mess of the descending drop pods and the ships in relatively low orbits for ground support operations.
Not to mention interesting strategic options, whereby you could pour defences into chokepoint systems with the aim of using it to draw away an enemies fleet and ground strength in order to fight a long slow siege to wear down the planets defences. Or have rapid reaction forces of mobile infantry units supported by Ground to Orbit Laser battalions in fast transports, designed to jump in with small fleets on the frontier, land on mining asteroids/early stage colony worlds. The hope being that the GOLS battalions have the punch to catch whatever relief forces an enemy sends out off-guard, and either delay the retaking of those positions by dint of forcing them to be wary and call in reinforcements. Or blow up their initial force and then force them to either cede that ground or send another force to retake it.