I myself tested and confirmed for 1.9.4, 1.10.2, 1.11.2 both:
adult zombies hit through corners of a (diagonal) wall (sometimes an arm can be seen) and
adult zombies hit through a closed door.
Maybe it's not attack radius but something like hitbox or gaps or solidity of the object(s) between attacker an mob/player. (Seed -5821562820736002727 on 1.11.2 generates a village near the spawn - all villagers die because in the houses they are not safe against zombies.)
For similar description see the duplicates (whose problems are not solved, but there status is "resolved" only because they are duplicates).
My details: I tested with zombies on one side and villagers and player on the other side of a wall. I tested some types of stone and wood - all the same result. Hitting through the door is not affected by the orientation (inside/outside) of the door.
X = block of the wall D = door (tested in both directions) Z = zombie V = villager (same with player) o = nothing special (monospace did not work here)
oZXZo ZXVXZ XVoVX zombies hit villagers ZXVXZ oZXZo
ZZZZZZ ZXXXXZ ZXVVXZ zombies do not hit villagers ZXVVXZ ZXXXXZ ZZZZZZ
XXXX XoVDZ zombie hits villager if both near the door XXXX
Ambiopteryx
I myself tested and confirmed for 1.9.4, 1.10.2, 1.11.2 both:
adult zombies hit through corners of a (diagonal) wall (sometimes an arm can be seen) and
adult zombies hit through a closed door.
Maybe it's not attack radius but something like hitbox or gaps or solidity of the object(s) between attacker an mob/player. (Seed -5821562820736002727 on 1.11.2 generates a village near the spawn - all villagers die because in the houses they are not safe against zombies.)
For similar description see the duplicates (whose problems are not solved, but there status is "resolved" only because they are duplicates).
My details: I tested with zombies on one side and villagers and player on the other side of a wall. I tested some types of stone and wood - all the same result. Hitting through the door is not affected by the orientation (inside/outside) of the door.
X = block of the wall
D = door (tested in both directions)
Z = zombie
V = villager (same with player)
o = nothing special (monospace did not work here)
oZXZo
ZXVXZ
XVoVX zombies hit villagers
ZXVXZ
oZXZo
ZZZZZZ
ZXXXXZ
ZXVVXZ zombies do not hit villagers
ZXVVXZ
ZXXXXZ
ZZZZZZ
XXXX
XoVDZ zombie hits villager if both near the door
XXXX
(Many villagers were harmed during this test.)