I clearly recall putting 'pea gravel' into any sand filter, up to about 1/2" to 1" above the laterals before adding any sand. Al is certainly right about having water in the filter before adding sand (and, as I suggest, 'pea gravel'). Perhaps it's because adding the pea gravel might hide a broken latteral. However, I recall the PacFab Triton (?) filters recommending doing this.
This makes sense, the top 12 - 24" will catch as much "stuff" as an extra 1" (or so) will, and you get a less constricted flow around the latterals. (And if a lateral breaks the sand into the pool will be lessened, perhaps allowing the owner to postpone a lateral replacement a season)