You use the words "lower body" and "upwards and backwards", but that only makes sense if I am looking at the model from the same direction as you. In the model there is a superior and inferior body and directions +Z and +Y. You should use these terms as they are unambiguous.
With Z axis up, the superior, which is Fixed, is on the top of the inferior. The force is on the inferior and pushes it in the +Y direction, which I think is what you mean by "backwards".
Since the line of action of the force is below the angle of the rigid link, I expect the lower body to move downward (-Z) and it does.
I also don't think the force should be on the post. The force is applied elsewhere. The post picks up the contact force from the rigid link.