Distance from Air Filter Above Carb to Carb Top??

If someone was going to mount a flat panel style filter element straight above a carb, how far above the carb should the minimum distance be? Or like a filtered air filter lid only without the rest of the circular filter element. Is there a standard distance to smooth out air flow? Carb/s would just be pulling straight down without bends or corners like a traditional round air cleaner. I am trying to lower overall height of my set up to fit in a hood mounted scoop better. Any thoughts would be greatly appreciated.