While sorting out my problems at the weekend I put a compression tester on the engine. All good, every cylinder giving 13.5 to 14 bar.

Checked the Haynes manual and they quote 11-13bar.

I am guessing that either the gauge is slightly misreading, or the head has had a skim at some point. Engine had only done 44K miles but it did look like it may have been off before.

Compression will also depend on cranking speed, could be carbon buildup

Also depends on the ambient pressure and temperature.