Slightly larger, with less pitch...hmmm...where have we heard that before...D-U? Dar?

FWIW one of my Webra .50's was like your .55, with very little pinch and almost no base compression. I ran the first gal. of Powermaster 10% sport fuel through it (flew it ) with 4 oz. of extra castor added to help put a little varnish build up on the piston. The extra oil also helps seal things a bit.
As you might imagine, 1 gal didn't put much varnish on it, but it helped, and after another gallon, it has great compression, and has excellent throttle response. You can see a nice, golden brown coating on the skirt area of the piston, just below the top edge.

How does the compression feel, and how quickly does it leak down if you put some oil in the cyl.?