Budyonny has 152mm guns, so afaik it needs 26mm of armour to arm its AP fuses. Leanders (that same example you game for the sake of consistency) armour (excluding main belt) is 10, 13,16 mm on superstructure, bow / stern, midships respectively. 152s overmatch 10mm, so at least you won't autobounce on both ends of it.
So to arm fuses on those armour zones you need (values are given with 0° being perpendicular a.k.a. perfectly broadside):
10mm - 67.38° (add in normalization and it comes up to 75.88°)
13mm - 60° -> autobounce
16mm - 52.02° (add in normalization and it comes up to 60.52°) -> autobounce
See the problem? Your guns are in the area where they aren't big enough to deal with the 13 & 16mm armour effectively, but are too big to arm their fuses at those broadside shots.