In order for blending to occur, you need to blend from one animation to another, meaning they both need to be playing in order to blend. Otherwise you're simply blending an animation onto a 'pose'. In which case to achieve something like that you can possibly blend it using a looped animation of a single pose with beginning and end keyframes.
Without knowing your whole project, your best bet, imo, would be to use a
BlendTree from the
AnimationTree node. You can make a animations blend together using it's
Blend3 node and control the amount of blend in the