I have just finished plumbing in a Penair TR140C Sand Filter and have put in 275#, per spec, of 1/4-1/8" pea gravel. The gravel, wet, is just above the laterals, perhaps a half an inch.

Is this the correct height, or should the laterals be exposed and by how much?

The sand will be next, once I am satisfied this is the correct gravel level.