I think my Formost is about 1/3 of a circle or 120 degrees. It is sheeted so they can't see thru and stay calmer. My cattle know the way out is through the alley and chute and usually the problem is more than one headed into the alley at a time. When I switched from the original bar grate to a solid sliding door between the tub and alley and alley and chute problem solved.

Occasionally a young calf who has not learned the drill yet will be facing the other direction but if you don't push him too hard and open the first door to the alley they will always turn around to follow their buddy who just went through the alley/scale. 

Unless you have a long tapered alley section which gradually gets narrower as I have seen on some large operations there is always the possibility of an animal being in the tub facing the wrong direction. Just not a major issue from what I have seen. jmho.

Jim at Dawn