I talked to my judge friend about this at length regarding the sit spin on bronze - at the time I was having an issue with my left knee and could NOT do a forward sit low enough (it's thankfully not an issue now) but she did say that while it would be unusual to see a back sit at that level, there wasn't anything that specified it wasn't allowed, but she did elude to the fact that it would need to be darn good not to be questioned. I presume that the same would hold true with a back camel.