I don't have B roulette stamps.
These were issued last on December 6, 1945.
My hypothesis is that due to the difficulty of detaching the stamps from the sheet, they changed the thickness of the knives and their inclination so that the distance D1 is smaller.
I don't know where the name zig-zag roulette (B) came from, but it seems to cause confusion.
I compared your picture with type AB roulette.