Command tests: Base chance = global or local supply?

[Mowgli]

Hi guys!

I'm currently in a PBEM in FWC:Serbia 1914, playing the scenario #1914_0917_01 Jarak as the Serbians.
Despite a global supply value of 40% and decent commanders that are stationary (no OOC due to movement) and well within command range of each other, my HQs fail about 90% of their command tests. On average, my HQs have been active perhaps once or twice in the 14 turns played so far.

So I wonder: Is this all just an impressive streak of bad luck on my behalf? Or is it that command tests work differently than described in the manual (p. 61)? My suspicion is that the command tests use LOCAL supply (which is about 10% for most of my HQs' current positions due to bad weather and mediocre supply sources) rather than GLOBAL supply (40%)?