Just purchased the Maxxair vent cover and while measuring to attach the clips noticed that the vent cover restricts the vent opening by about 3" (from 7 1/2" down to 4 1/2"). Is this typical? The vent is standard 14x14, no fan.
Yes they do restrict the opening a little, but well worth it.
Mount them as far forward as possible to allow for maximum opening of the vent lid. The farther back, the sooner it hits the sloped area of the cover.
If you look at the free opening of the factory lid even at a lower angle, it's still greater than the free area to the MaxxAir slots, so you're not losing any additional airflow capabilities with the factory lid opening slightly less.