It's not so much about compression, but a series of parts that influence the vacuum signal and air velocity. Intake, exhaust, cam, heads- everything works together as a system and the intake plenum volume is part of that system. That's what spacers are doing: adjusting the volume of the plenum. If you've got the time and $$ it might be worthwhile to try a couple different ones but it's not a big issue by any means. You needed clearance and you have it so I'd say you're good to keep the train rollin'. Keep up the hard work, you're making more progress than I am.
