My older QH gelding will scramble if he's tied to the right hand side; no
problems if he's on the left. Fortunately, my Arab prefers the right. I
have a 4 horse trailer with a partial divider between the horse side to side
and a full divider between the front and back horses. I also found that the
partial divider was better than the full divider for scrambling. What I
found interesting was that this QH I had hauled all over when he was younger
but developed the scrambling behavior around age 20. (28 now) I went
through a trailer-less period of several years so maybe he "forgot" how to
haul?!