You always want compression thats a good indication. Pinch is a different story that when you have metal to metal contact from your piston making a stroke in a sleeve. Break-in seals your Piston and Sleeve as you move past the break-in the pinch goes away this forms compression.

a Glow plug shouldnt effect compression as far as I know but it will alter performace. Did you have a copper glow plug shim on this or prior plug?