Yes on all accounts.
If you want to center the plates on the part of the bed south of the pillows, then just adjust the measurements for the centering, tucking, etc.
I've had some bed quilts where I didn't attach a top border, or did put one that was substantially smaller than the sides and bottom.
If I didn't need the length, there really was no need for it. As long as it covers top of the pillows a bit, it was fine.