It's the same with box stalls.
I only have ONE that will actually stand in her own manure or urine. My other 4 pee and poop up against the wall in the back so they don't have to stand/ walk/ lay in their own yucko. Of course my mostly WHITE horse is the one that will take a nap in her own piles of yucko. I always thought there was something amiss with her because of this... I guess she's normal and my other 4 have OCD