Poor Ricky.
Teddy had a lot of booty washes his first couple of years with us. Part of it was that he was a nervous pooper.
Secondly, when we took him places, he would get so excited that his stool was looser.
I think it is less about the hair and trimming, and more about the stools and whether they are too wet. Also the behavior of the dog -- is Ricky in a hurry to run away from his poop and maybe doesn't squat long enough? That was part of Teddy's problem.
The problem was made worse because Teddy was fearful of pooping and having problems that would require a booty wash. When things starting going right, he gained confidence, calmed down, and took his time to do his business.
It does help to keep all of the hair on the back end, including tails and legs, combed. Tangles can interfere. You can band the hair on the back end. Just make sure that no hair pulls and that Ricky has full range of movement.
I think Max has only had a problem once in his entire life with us. He knows how to squat and he stays until he finishes.