It's normal for it to dissapear when your decelerating.
You should be at least a lil rich under WOT. The ONLY thing you really need to use the guage for is making sure your not leaning out. Get the car on a dyno while under spray, and be sure your not leaning out, that your pump isn't giving out on you high in the RPM range, or that your not maxing out your injectors.