Also, if your combat units are battalion sized, the cost of a command unit with 5-6k command capability is negligible. Its another thing if your base unit is brigade-sized and the command unit needs to control 25-30k.

If you want to get technical about it, the cost of the command unit as a relative fraction of the cost for a base formation is basically constant (neglecting armor, base unit class, capability modifiers, etc.) up to 50,000 tons, since the cost of a HQ unit is still linearly proportional to the command capacity. If you have ten 5,000-ton battalions with HQ5 units, the total cost of command elements will be the same as if you had one 50,000-ton division with a HQ50 unit.

The excessive cost of HQ elements comes from two mechanics. First, and more obvious, is superior command HQs. If you have, say 3x 25,000-ton brigades and a divisional HQ able to control 100,000 tons, the cost of that divisional HQ is a significant premium, and you pay that premium once more for every higher level of your command hierarchy. Second, the size of a HQ component is limited to 250 tons (added, of course, to the size of the base unit class and any other components that might be mounted, e.g., VEH+HQ+FFD), but the cost scales with command capability, which means that the cost of a high-capacity HQ makes up a very large, even dominant proportion of whatever formation it is part of.

http://aurora2.pentarch.org/index.php?topic=11545.msg146507#msg146507

The link in question, for those who don't want to edit it.

The way the rules work out, you don't want to put multiple HQ units in a single formation.

Doubling the number of HQ units halves the chances that your commander dies IF the HQ unit is hit and killed...but doubles the chances of the HQ unit being hit. So it's a wash. But you had to build twice as many HQ units and they are expensive.

Actually, it very slightly increases the chances of losing a commander from a HQ hit, due to how the combat/non-combat unit math works out. Very small change, but this emphasizes that there is no benefit to multiple HQs in a formation.

Personally, I almost never use INF+HQ units, as the STA+HQ unit is much more resilient to fire even with light static armor. Static units have base 3 HP compared to base 1 HP for infantry which means in fact 9x better protection against the light infantry weapons (PW, CAP) which are very common. For the extra 12 tons on a unit you will only have one of in the entire formation, this is very good value. The only exception is that I will use a 10-ton INF+HQ for my boarding parties out of necessity.

Otherwise I will put an HQ on any level of vehicle to match the formation - LVH for 'mechanized' formations, VEH for armored/tank formations, HVH for heavy armor, etc. Any one is fine IMO, obviously heavier armor is good for staying alive but it also increases the cost of the HQ unit which can be a significant amount for larger HQs (especially over 50,000 command capacity).

Make sure to mark the HQ as a non-combat unit as it gives them a smaller footprint in the unit template when targets are chosen. For frontline units, I also give multiple HQ units so they can suffer a loss without losing command bonuses immediately. For me, the logic is the chain of command through company leaders in a battalion.

Like what type of unit should be the HQ? Obviously stationary for planet garrisons, but for landing troops would a heavy vehicle be best, and how do you assign a commander to a boarding party that has to be all infantry?