That much of a change in the 'good' direction does seem strange, but engine block temperature and ambient temperature can vary the ring-cylinder fit somewhat. Cranking speed (which also varies with engine temp and battery condition) may be responsible for some of the difference. Maybe you've been using better oil and filters? Or maybe some oil is getting past the guides, and the head is starting to get some carbon deposits?

Nothing to worry about, though - you won't blow the head through the hood. If anything, you're getting some slight increase thermodynamic efficiency (Carnot cycle) with an increased compression ratio.