It does make sense that the door/ area closest to other horses becomes the safe spot.
I normally have dealt with getting a horse used to going down to the far/ scary end of the arena by starting on a circle at the end closest to the door, and then slowly leg yielding the circle down or turning it into an oval so that we gradually got closer and closer to the scary end. The way this arena is set up though with the obstacles in it (very heavy trail bridges), it basically splits the arena into 3 sections, so I’m not able to just slowly leg yield over a foot every time we pass the scary end without something being in our way. I’ll try doing a looping/ cloverleaf pattern and see if we get anywhere with that.