Vampires Army Spawn Bug

I just realised, that Vampires does not get affected by the "-10 army spawn bonus" I saw this multiple times, but i never gave it too much attention. For instance, if i have a connected cluster of 20 regions, i still get 20 reinforcements.... shouldnt i get 18? 20 -10%×20 = 18
Maybe I gt something wrong and army spawn bonus is not the same with reinforcements gained after ended turn?
