OFB rack modifications

[tntxajun]

I am planning to add additional grates to my OSFB and was curious if there was a formula for how much height the first cooking grate should be from the bottom of the cooking chamber to ensure unrestricted air and smoke flow ? Would 2" be too low or should it be higher.

TIA
Jack~

 

[tntxajun]

Sorry, should have included in the original post, this is a horizontal offset
unit. 36" long x 16"wide. Also, how much distance is average between the
1st and second shelf?

TIA,
Jack