So maybe was it just two turns then ??? Bizarre ...
I think it was really three turns, because in my own tests, using the same factors, I got a lower supply than calculated, too.
Resupply is probably a daily dividend so for this scenario (depending on 12 or 6 hour turns) the nominal value is being divided 2 or 4 times before randomization.
I don't think so. First of all, use of supply (with exception to unsupplied units) is depend on MPs used and number of rounds participating in combat, which doesn't change with time scale. Making resupply a daily dividend would be inconsistent, since the use of supply isn't dependent on time. A combat round in a full week scenario represents a greater period of combat than a round in a half day scenario, but both cost 10 points of supply.
I ran some tests with the Korea scenario (full week) and the calculation is on spot. 33 of hex supply level, multiplied by 0.67 (33% less for "no high supply") multiplied by 0.75 (distribution proficiency), I get 16 and that is exactly what the units that didn't move got when on railways. The problem must be the night turn thing.
Quoting the test I did above:
I did the same test in Arracourt scenario, but with a single turn. Ended my first turn on railway with 58% supply and 16 as supply value for the hex. 60% formation distribution efficiency and going from AM to PM turn.
16 x 0.67 = 10.72 (no High Supply)
10.72 x 0.67 = 7.18 (night turn)
7.18 x 0.6 = 4.3 (proficiency distribution)
If, instead of multiplying by 0.67 (to reduce supply by 33% for night turn), I multiply by 0.33 (to set supply to 33% of what I would get in night turns), I get:
10.72 x 0.33 = 3.54
3.54 x 0.6 = 2.1 (proficiency distribution)
This is exactly what the unit got.
In fact, nukkxx three round tests would bear 7.6 for day turns and 2.5 for night turns, if calculated this way. If he got 2 night turns and 1 day turn, we get 12.6. But, if decimals are discarded before adding to the supply of units, we get 7+2+2, which is exactly the 11% he is getting for the best placed units. Ok, this was some exercise in fitting numbers, but since we don't have access to the inner workings.
Resupply levels are reduced by 33% during night
Turns.(from the manual)
Maybe they are being reduced to 33%. Obviously, this is just speculation.
In fact, I think that factors independent of units or units interactions like night turn penalty and the "no high supply" penalty could be reflected in the hex supply level number; that would make things easier for player to calculate how much resupply the unit will get next turn.
Did you remember do multiply with 2/3 for non-adjacent HQ?
Adjacent HQ give a boost of 50%, if cooperative. As far as I know, there is no penalty for not being adjacent to HQ.
The level of resupply possible for a unit increases by
50% if a cooperative Headquarters unit is located
with or adjacent to a unit. (from the manual)