Hostile mob pathfinding poorer than 1.8.9: mobs now confused by vertical separation

I have a fort that is on a big slab at the top of a large fairly steep hill. The slab is bigger than the top of the hill. If you climb the side of the hill (nice easy slope, no problems doing that) you reach a door that's near the middle of the slab to gain entry. I can stand at the edge of the slab and look down (30-ish blocks) to surrounding territory. See attached cropped screenshot.

In 1.8.9, hostile mobs (zombies in particular) would spawn in the surrounding territory (like the flat spot on the left side of the screenshot) and, if I caught their attention and they were close enough, they would pathfind up the hill to the door (and sometimes start beating on it). This would occur regardless of where on the slab I moved to - they could figure out they needed to go through the door to get to me while I was up there.

Now in 1.9 they pathfind quite reliably to the spot on the terrain at their level that is directly under wherever I am standing, and stand motionless there looking up at me. If I take a few steps to the side, they shift just enough to get directly below me again. They are no longer smart enough to pathfind up the hill to the door.

While I realize zombies are inherently stupid, and it might be a bit much to expect them to be smart enough to know that to get to that tasty bit of meat up there they have to walk around and up the hill to a door they can't see from where they are, it was sure a lot more fun when they behaved that way.

I also see that Endermen now notice when I'm looking at them from above (they didn't in 1.8.9), but they display the same poor pathfinding behavior: they move or teleport to directly under me and stand there glaring up at me angrily and vibrating.

Was this change intentional? It would be nice if the more-complex (and more-effective) pathfinding behavior could be restored.

Thanks!

Potentially related: MC-89006 (but no water is involved in my case)