water height in overflow box

[Chad]

Any chance you have a photo of your overflow box?

I got the general idea. I guess what I am after, is I'd like to make the overflow box as small as possible.. so, I have a max return of 200gph.. in a 18 by 14.4" tank.. Using 3/4" piping.. I want to get the overflow box height as tiny as possible, but I have seen so many peoples overflow with 2 or so inches of water ABOVE their normal overflow drain.. with still an inch of so more before it ever reaches the emergency. So, what causes the height above the real drain to be higher than the actual inlet? I would think if it was a matched flow it would never be higher.. am I just cookoo? and not seeing something?

Thanks for the help!

Chad