Hardcore supply (and normal supply for that matter) works by pretending that the supply is a unit with 250AP points.
For Easy Mode Supply, it starts at STAVKA/OKH and moves directly to the unit following the easiest path. Rail lines are essentially 0 (in that you can move several hexes along one for only 1AP cost). Roads are 1 AP each to move along. Clear hexes are 15AP. Crossing rivers are either 25,50,75 or 100 depending on the size of the river.
For Hardcore Mode Supply, that virtual supply unit has to move from STAVKA/OKH to FRONT/ARMY to ARMY/CORP then to the unit. But the lower level HQ's pay 1 AP for the Rail, and 3 AP's for the road...the rest are the same.
When that Virtual Supply Counter gets to the unit, the actual amount of supply will be a percentage. If you spent 100 AP's or less then you get full supply. If you spent 100-150 then you get 75%, if you spent 150-200 then you get 50% and if you spent 200-25AP's you get 25%.
Essentially, if you get full or 75% supply, you should have lots of AP's for your units, and attacking will be pretty much normal. At 50% you will notice a drop in AP's, and can do some limited movement, but probably not attack. (or sit and defend). At 25% you will be dislodged from your position fairly easily.
If you think of the two ends of the scale..at one end, we have roads in every hex. At the other, no roads....
With roads in everyhex, supply becomes trivial, as you can be 100 hexes (1000 km) and be in very good supply (75% or 100%).
With a connected road net every three hexes, you will always be within one hex of a road, which drops the range to around 85 hexes.
With a connected road net every five hexes, you will always be within two hexes of a road, which drops the range to around 60 hexes. (thats 600km). I feel that this is pretty much what the game is giving us.
With no roads at all, you have to be within 8-9 hexes as the supply movement costs are more. 80- 90 km away from your HQ.
This is assuming clear hexes and optimal placement of HQ's.
Something I havent mentioned yet either, is that logistical centers will subtract AP's from the movement cost...but this usually just help reduce the STAVKA/OKH to FRONT/ARMY portion of the trip to less then 15AP's (if the front/army hq is on the railline)
I feel that these roads on the map are roads capable of high volume traffic, as you can and will be supplying whole armies along them. The small scale roads, manufactured roads, country roads etc....are represented by the 15AP cost to move supply over clear hexes. The game will allow us to adjust that number for both Soviets and Germans, so we could have a different number if it could be shown that the Russians were more adept at moving supply cross country. In fact all the costs could be different for both sides.
In practice (probably around 120 turns of playing so far) my friend and I have noticed that the soviets suffer more from the Hardcore rules, due to Geography, and army size/HQ ratio. And in winter, Geography will no longer come into play as rivers become frozen and free to cross for supply (like having a bridge in every hex). And the Russians could have more HQ's built...so when the Russians are on the offensive, they should not have supply problems.
“My logisticians are a humorless lot … they know if my campaign fails, they are the first ones I will slay.” – Alexander the Great