These is what I do since I got this answer from master tuner Dennis Richey several years ago. Hope it helps as it has been to me.
AFM
Don’t confuse compression with pinch; Sleeve Pinch is not that important contrary to popular belief. The question is how well it seals as soon as the piston starts to close the exhaust port and if it holds compression after you roll it to top dead center.
Place a few drops of after run oil trough the top (removing plug), then place plug in place, then roll piston to top dead center and listen and look for air bubbles through exhaust port. If there’s none, then your engine still has compression, even if it has no pinch.
The fastest team motors we use, have zero pinch. I even had them run to over 140ºC and they have survived well. Though I certainly don't recommend it.
Dennis Richey
Richey Racing Engines
I understand his reasoning(and Yes, I know who dennis richey is, wonder what happened to him), but the problem with that test is that when the engine heats up all that changes. Whats important is how it seals at running temperature, as both the sleeve an piston expand.