ground combat suggestion for aircraft and AA:
The current system is that light AA targets the planes hitting its formation. Medium AA can hit that + one lower formation. Heavy AA hits all planes everywhere. Heavy AA being able to target unlimited everything makes it a no-brainer choice in every situation.
Basically the idea is to make it that each AA unit covers formations with the same rules as above, except that it covers a fixed amount of tonnage, and going over coverage reduces effective hit rate equally proportionately, (no loss). For example, two light AA's that cover 5000 tons at 50% is the same as one heavy AA that covers 10000 tons at 100%. Consider the size of the front, if you having an interstellar invasion, the battle will be on fronts spread out in squads all over the entire planet against low flying aircraft hugging the ground.
Basically what I want is that heavy AA is less coverage efficient than using many medium AA even if it targets everything. Maybe medium ones cover efficient, and maybe small ones best fit every crevasse, and heavy can hit units on CAP, or something like that kind of like how heavy arty's special feature is being able to hit backline. Maybe you can make it that small AA's are normal at 100% coverage, but going with more size than its coverage 10% worse than a proportionate amount, whereas heavy is the opposite, where anything beyond its coverage is 10% less better than the proportionate, such that for heavy you want to be over your coverage, and using this you can create some kind of interesting dynamic. I have a feeling that won't be necessary though, and just making smaller ones simply cover more does the same trick.
I also think AA guns should have uridium costs that scale based on their tracking speed too, so ships aren't paying extra on those engines for nothing, and should simply take the nerf both of these changes causes. Fighters are expensive, they require expensive hanger space, FFD's and maintenance facilities, yearly msp payments. They could be op, and you still might not want to use them because you'd rather spend your vendarite. They shouldn't be quite as easy to kill with AA as they are now - after all if they were just a little higher in space, they wouldn't be hittable at all - or at the very least would be only hittable by reasonably damaged weapons that costs not-vendarite. . . AA damage like all ground units hyperscales with technology for free. That means past a certain point, armor on fighters is basically a trap you're guaranteed 1 shot if hit (nothing about ships gets cheaper with tech, just lighter, but ground units do get straight up more efficient). I think planes need to be balanced around getting one shot tbh because there isn't really a satisfying way to fix the AA hyper damage, and honestly, fast jets make sense and it can inadvertently balances things. I also think a plane perfectly designed against its target on ground support should destroy that AA cost-efficiently and over-all function cost efficiently. It should only be (very) cost inefficient when trying to do the same on flak suppression and the like, or else really, why waste the FFD on something that is simply worse? Remember, AA still functions as a ground unit! they really really effective!