I know the top part is not a full block, but I think it still should be part of the hitbox -if technically possible- for three reasons:

1. I can just chill right inside it, what looks a little bit weird, but it's the smallest problem.
   

2. Z-fighting.
   

3. Other ao, dynamic lightning related problems (this might be situationally worst depending on Sodium, Optifine, Shaders ect. but inherently it's vanilla problem)
   

Overall, all of them are small visual problems only, however if possible to do, fixing them would be still a nice improvement.