Ok, something else I can't figure out. The rules say:
Corps HQ must be within 20 movement points of rail, and hasn't moved. Check. HQ Buildup button is active.
Attached units within 5 hexes will be counted. Not check. I've got an HQ with 4 units that says it has 1 attached combat unit, and an HQ with 3 units that says it has 0 attached combat units. The units have moved and fought this turn, but they are all within 5 hexes. What am I missing?
And, second question: Deep in the strategy and tactics notes (25.1.1) it says, "the overall supply to your whole army is reduced by about 1-2% for about 2 months for every time you use it."
Is this an additional cost, not described in 20.6? Or is it an ad-hoc estimate of the consequences of drawing extra supplies from your network of city depots? If the latter, it seems an over-estimate.
(~50 Corps)*(0.015)*(8 weeks) = 6 Corps*weeks of supplies. But if it's an actual (poorly documented) cost, then HQ Buildup looks very unattractive.