I don't know why leaving the static on the Piper blade seems to cause errors, but we do an awful lot of Pitot/Static checks and I can tell you with good authority that they are almost always (obviously not all the time, because some people get by) less accurate when installed with the static plumbed to them. Of course you'll never notice an error during a pitot/static check because the box is plumbed relative to the instruments and they will always match. But, that being said in flight my experience has been over the years that they are almost always less accurate (even by a small margin) and do in fact have errors that many times the pilot doesn't even know he has. You won't see any obvious problems, because relative to your plane you won't know you even have any errors to begin with.
The fact is that again, almost always the Van's standard pop rivet ports are the best solution for static ports on these RV's.
My 2 cents as usual!
Cheers,
Stein