I am a bit disappointed at the current representation of partisan warfare in WitE
first of all, they seem to have a very binary effect: if they cut a critical railline, they can jeopardize a whole sector of front. If they don't ( whether they just out in the countryside or sitting on a railroad that can be bypassed) all they do is picnic and catch butterflies.
Since by 1942 the German railroad grid is probably fully converted, partisans are only a serious threat in 1941, which is actually the year when they did not constitute a significant threat.
In addition, I believe that the impact of partisan warfare in real WWII translated into cumulative attrition losses by harrassing rear echelon troops, blowing up supply depots etc. Not particularly by shutting down a whole sector of the front by blocking all railroad traffic for one whole week.
Honestly, I think partisan attacks should result in attritional losses for trucks,supplies&fuel (destroyed in ambushed vehicle or railroad convoys), and a few German blown up in the process (trucks are currently immune to partisan ambushes). This could be abstracted and taken directly from the pool. And a small temporary reduction of the rail cap, simulating delayed railroad convoys.