skimmer water hieght in sump

[js198027]

I am planning on building a sump out of a 40 gallon breeder for my future 75 sw . I was thinking of going skimmer/refugium/return. I am looking at getting the Ocotpus Diablo DC 150 Skimmer. It says recommended water depth is 5.5"-6.5". My question is can the water be over this level and still have it work. I would like to have the water level higher in the fuge or can that be controlled with the glass baffles? i am new to the salty side so trying to learn all I can with minimal mistakes. Thanks for any help you can give me