Carl,
Mortar shells are lifted by their ears and lowered into the short bore and released.
Note, in the Mordecai plate of strapped shells that the rope is attached to the straps for ground moving. Since theshells would have to be lifted up to the bore by a davit and pulley, by having the ears off center would present the wooden sabot to the bore.
Does this make since?
Also note that the strapped shells are for seacoast howwitzers and columbiads.
No reference for my statement just applying some physics.
John