Skeleton "hitbox" too big

When a normal skeleton (not wither or stray) is in a 2x1 space, you can't place a block above him (or bigger space, 2 high air gap). What I expected is: that i was able to place a block there, as with pc version 1.10.2.
How this translates to other mobs sizes I don't know, because of the various mob sizes and i am unsure how to check their size.
It doesn't matter if the skeleton has a helmet or not.