Gravel level with respect to laterals: TR140C Penair Sand Filter

I am installing a Pentair TR140C which specifies 275# of 1/4 to 1/8" dia pea gravel. What I find is that, when wet, this amount just matches the height of the top of the laterals. Is this the right level, or should be laterals be covered to perhaps an inch or should they be exposed? The sand will go above this obviously, leaving the needed free board of 13.5"

Please do not double post the same question in more than one place on the forum. It is easier for people to help if all the replies are in the same thread. I am going to lock this thread and let you use the other one you started.

Good luck! :)