Jdean - to answer your question best, we'd also need to know how it reacts under full throttle at a couple of different RPM's (3000, 5000, 6000).
If you take fuel off at the top to correct your problem (your secondaries), it could adversely effect your higher RPM/load operation. If you take it off at the bottom (your primaries), it could adversely effect your low speed mixture/performance.
Your powervalve does not effect mixture at cruise, unless you have unusually low vacuum, and that is activating it.
Having said all that, I would guesstimate that reducing your Primaries a little bit, should improve the cruise mixture.
91 Crown Victoria Ex-Police -- 460 powered! 14.3 at 97 MPH 1/4 mile with stock tires, 4000 lbs, stock 78 Town Car converter, C6, 3.08 gears.
87 Mercury Cougar XR7 -- T5 trans, 400 RWHP, supercharged 302!