From: Utlima Thule
some of this no-one knows (well maybe Gary), so to quote 25.11 the "standard Resupply/Replacement segment is broken
into many smaller segments" - great but we don't have a list of those segements. So there lurks a fundamental problem, its one of those bits that are out of sight.
But in general the sequence for combat formations is:
a) try to supply priority 1 HQs, even within this there is a bias to lower priority HQs (this means that they have a decent chance of getting the 30% they need)
b) ditto for priority 2 HQs
so no manpower 90 can mean a few things, it has failed more than once or it failed at the third check
now running across all this is endless leadership checks esp vs admin scores. Worse these are influenced by the support squads and CPP values.
Now the Soviets are plagued with low admin leaders and a lack of support squads. If you have high CPP this offsets a lot of this as "CPPs affect the chances of passing administrative rolls for resupply" (23.2.3) - but note again there is no given formula (unlike for the relationship between CPP and MP).
In effect, a Soviet unit that is poorly led, badly placed (wrt depots) and/or low on CPP is going to miss a lot of supply checks regardless of what is in the pools. To get replacements into those units, you probably need to use the refit mode, and get them close to a depot. To make this worse, the supply routines will push fuel/ammo/supply first and then replacements (so again if your units are at the end of a poor supply chain they will see few if any replacements).
So accepting there are regions where you need to be (Valdai, Volkhov, Caucasus) where the supply system is stressed what can you do? Well you can't assign your few competent commanders (you prob need them somewhere else), you can manage your CPP, you can rotate units back to depots to refit and return to the front. In an extreme case, you can allocate a rifle brigade and merge it with the target rifle division (there are places/times when this is essential)