Hand rotated backward when using blend poses by bool

Sometimes it chooses to rotate backward instead. Can somebody point me to the right direction?

i cant read the values in the video, but i think that when his arm is back its technically rotated closer to go around that way then to go the correct way. i think the answer is to make a 1d blendspace for it. Also hopefully your game will be what mighty no 9 promised. good luck!