Air bleeds

I thought I read that the air bleeds could tend to lean out the mixture as the RPM rises up to redline. I know it's sort of a voodoo trial n error testing thing. I think it was Car Craft that did an article of a '67 barracuda with a tunnel ram, and they were using Pro-form Holley style replacement main bodies with cool removable air bleeds. After a lot of dyno testing, they did pick up quite a bit more power on the top end and eliminated a high RPM rich condition.