Okay, so. To lay out my thoughts I'm gonna go through my decisions in this plan to try and make my inevitable failures in planning to be more obvious.
First off, this isn't a real war, it's a survival mode. If we had the ability to guarantee we'd hold out until naval reinforcements arrived while killing zero kids personally, I'd take it without hesitation. We cannot hope to wear them down on the ground side of things, and since the only thing limiting the Nids is throughput they're worthless to kill.
Secondly, biomass is worthless within the timescale we're operating on right now. They make new ships within the timespan of weeks and we can't hope to ever kill enough Nids on the ground to make a dent in their biomass supplies anyway. This would mean that we could staff the cities with skeleton crews to chew away at the naval battles and just take the hits if holding ground wasn't also a vital component of success here.
Thirdly, I suspect the Nids will be attacking in spearheads, hitting the more lightly defended areas and ripping through them with the power of ludicrous force concentration. It'd fit their new adapted MO and, in general, the Necrons probably punished spreading out their forces via the medium of stamping them into the ground. Man, thank gosh for N Steps Ahead letting us have retroactively put hero units in vulnerable zones.
This boils down to my plan for moderate defences for our non-core cities and hives. Letting the Nids just roll over the cities would waste the troops and secondarily lose pieces of orbital support for every place destroyed, so some defences would be optimal, but in general the Nids will be hitting us at our main base and once they do we're gonna be facing the issue that a majority of our non-hero troops will be stuck ambling in their own, far less vital cities, while the Nids hammer us at our core.
That said, writing it out it seems like pretty much no matter what happens we're gonna be eating overcrowding penalties. I doubt they'll offset the fact that we'll have legions of gunwalls, but that does make me lean more towards spreading troops out to the borders. So I'll lean towards stacking troops to the outer regions anyway.
Sadly, I don't have anything really clever to consider adding to the plan, so chuck me any suggestions you can think of.
[X] Plan: Rolling With The Punches
-[X] Garrison each city with a Corps(30 Armies total)- Enough troops to operate the cities fixed defences and to hold for a period against even a sustained assault. Additional AA and anti-orbital firepower while the city holds.
-[X] Garrison each Hive with half a Army Group (460 Armies total)- Enough troops to operate the hives fixed defences and to hold for an extended period against even a sustained assault. Additional AA and anti-orbital firepower while the hive holds.
--[X] Garrison Hives with Mixed forces- Fixed defences have full impact, will hold for reduced period.
-[X] Write In- Stand your ground, shoot with all AA in range, use air only to prevent enemy landing within your lines, and use one of the generalised Anti-Ground Tyranid poisons.