While testing for the smallest possible stall size, I realized that placing the hay rack and trough on top of the horse bed works just fine, so having 4x4 stalls is possible.
You need moveobjects to place both feeding items and the door to the stall, but horses can then enter, exit, eat, drink and sleep (including laying down) with no routing issue.
I think it only works from one side of the horse bed, but didn't test extensively to confirm.
https://i.imgur.com/MfkWVVv.png
https://i.imgur.com/5wBE6C9.png
(I obviously do not condone confining real horses to the smallest possible space, fortunately sim horses know how to open doors)
The Sims Team
