OKW has a MP float because they have nothing to spend it on.
No, OKW have MP float, because they don't have nearly as much attrition as any other army as their infantry scales defensively to the level of being overpowered compared to any other infantry survival in game.
You know there is something wrong when cheapest main line infantry got as much survivability as doctrinal specialized close range squad once it gets few vet stars.
Moreover OPsoldaten only widen the attrition gap because unless you blow then up with tanks, they will cause much more mp attrition then they will take, widening the MP difference even more.