Q: Supply and Resupply is only affected by a few things:
1) .rdp
2) resupply missions
3) tier
4) cutoff
5) end of mission
-Alphie

DOC:

1. Depending on how damaged your factories are, resupply can be delayed up to 100%, effectively halving your rate of resupply of attrited units at 100% factory damage.

2. If players move units up from the Divisional HQ to any of it’s Brigades (spawning at Div.HQ and despawning at a Brigade town under that specific Divisional HQ) they speed up resupply of that unit through “overstocking”, putting that unit despawned into the Brigade list outside of and in excess of the system run resupply train. The maximum is 50% oversupply.

3. As each new tier of equipment arrives the previous tiers best equipment experiences an increase in number while the lower level equipment and equipment from 2 tiers back starts to disappear from the lists. This allows the battlefield to be populated by a gradual shift in equipment status rather than an instant “everything is the latest” changeover. This performs another useful function in addition to pure immersion (the gradually changing state of the battlefield shifting as time goes by) when the enemy is spawning only the older equipment it’s a telling sign that you have attrited all their newer equipment, in general. This is not just immersive it’s good de facto on the spot intelligence for those fighting a difficult and long drawn out battle, on the localized state of your opponents supply and ability to hold you off.

4. The factor that determines a brigade or its Div.HQ (or both of them) getting supply or not is twofold. System run “train of supply” stops when your formation’s base town of operations (where it is located at the moment) cannot trace a friendly line of links back to ANY of your RDP factories, it only needs one factory “link” to exist to be supplied by the system. The second element is player run resupply. As long as the Div.HQ is not cut off from your RDP factories players can manually run resupply to a trapped/cut-off Brigade under that Div.HQ to keep it “alive” and in the fight to regain its supply links thus allowing it the opportunity to escape the encirclement.

5. If you get an RTB status at the end of your mission (despawn) the unit you were using is returned to the spawnlist immediately. If you are rescued a small delay of 15 minutes is added to the units time to return to the spawnlist. If you are listed as missing (MIA) or killed (KIA) the unit is never returned to supply and must be replaced by the system run attrition resupply which is set currently at 7 hours.
 
Distance “from the front lines to the factories” is not a factor of resupply in the game at this time. It might become a part of resupply at some future point in time. There is a small but worth considering effect of moving the non supply link related formations (air-forces, airborne army and navies) back in that they tend not to attrit as quickly and are thus better supplied and hold higher average stocks of supply if they are further to the rear, and used to resupply frontline units that are being mowed down at much higher rates of attrition. Enemy units looking to attack these brigades in the rear (common with air force units) also tend to suffer higher rates of attrition than when the fight is closer to their own airfields. While these kinds of effects are not obvious they can over the long term have a profound effect on success and failure with regard to running out of equipment before your opponent does. The side with equipment left fighting when their opponent has none, usually wins.