There are at least two good illustrations and explanations of the theoretical operation of the doll's head in gun books (can't locate them at present but think maybe Garwood might have one). If the shoulders of the dh bear on the front shoulders of the mortise, the dh "triangulates" the flex of the action bar, as per Pipes description--another sort of tie rod. If the bearing shoulders are gapped because of the clever adjustment of the ball hinge such that the top lever looks nice on the right hand and the breeches and dh are proud of the fences and the mortise, obviously the advantages of the dh as a "holdfast" if not a "fastener" are lost.

jack