Sump questions.. need advice

[One_Divided]

I don't know how crutial this is, but I want to be safe and check with you guys. I'm making my own sump for the 50 gal. I need some recommendations on a few parameters..

I am trying to figure out how high/low to put the dividers on each side..



The skimmer is running on a mag 7 and will be returning from the left, to the main chamber. The eggcrate will be covered in frags eventually.
There will be about a 3-4 inch sand bed around 3-4" below the eggcrate. The entire sump is 13 inches high.

Thanks in advance for any help!