Well, more thoughts around of KISS principle.
Because those different preferable zones that I suggested this morning - that was stupid, but wasn't simple.
And I agree with
Hazard eventually: there is no way to have any other dominant terrain in
decisive fight (for transnewtonian civilization colony) apart from urban and suburban.
Therefore, there is no place, no relevance for detailed biome terrain types in surface battle for the colony per se.
You just cannot dig your infantry in those jungle mountains, when your (or alien) cities are placed on more clean terrain spots.
And there is no sense at all in training infantry at this dominant terrain, because there are
all those terrain types at the same planet of Earth! Just place your training camp at polar ice or at equatorial jungles, as you wish. Planets are not homogeneous - nor our Earth, nor other earth-like planets, nor those numerous tidal-locked planets (without dense atmosphere) of red dwarf stars especially!
For an StO transnewtonian fight, I can see only two factors, that I can cram into some Aurora AAR without disbelieve:
1. Atmosphere density, that is already realized in VB6.
2. Urban TN-masking. That is: if you see some noticeable TN signature on a planet from a space - you cannot understand if this signature is a military target, or it's civilian car, house, factory, etc, because those civilians use TN techs too. It's difficult to separate targets - not on the wild, but on the city, on the contrary! If you detect some heat or EM noise on the wild - you just aim it and blow it with your meson cannons, it's no problem at all, because if your fire control is precise enough to kill missiles at their velocities, than you aim any bunker without any trouble, the same moment you detect it, and there's no way to hinder you with such things as mountains and trees, that are just not TN signatures and cannot mask TN military activity, correspondingly. The problem is, that if you blow each signature on a planet - you will destroy the whole colony infrastructure, that is the most valuable asset on a planet, actually. Then you can just glass this planet with the same result.
So, Aurora troopers must fight on cities. And if you have low intel on the race that you attack, than you must have a penalty with separating military targets, because your men cannot understand alien common domestic forms and signs. It's all that must be count in decisive surface combat.
But! I see great area for guerrilla/covert operations in this dominant terrain! We have an
ansibles, so our spies and guerrillas can hide in difficult terrain to dispatch ships and stations orbiting this planet, eavesdrop enemy com traffic, make covert diversions against your civillians and administration, and so on. More difficult terrain - more infantry you need to clean this planet from enemy spies and guerrillas, or just defend your urban sites, especially on enemy home planet biome. And that is where those biomes are very important! Intel, exhaustion warfare and microbiological attacks. There are very important things, that can force you to glass this planet eventually, instead of having such prolonged, costly and potentially catastrophically troubles.
So, there are only 2 biome marks that have relevance:
1. Race, that have this biome as native. Earth biome = human race biome. Period.
2. Density of biome, that is set to 100% on the homeworld and is rising from 0% to 100% by terraforming efforts in colonies. (And I think that terraforming is seeding your biome, not spurting inconceivable volumes of gases from nowhere.)