Past experience. Back in the 80's my wife and I used to limit out on black nose crappie (a subspecies of black crappie in 2 to 5' of water all summer long. Black nose crappie are very aggressive and are easily over fished. I haven't caught one since probably 1995. During those later years we noticed we could still catch regular black crappie at the same depth during summer but only at certain locations. Spots that produce seem to produce constantly. Places that don't produce usually suck constantly. lol
The wife and I put out small brush piles in places that looked good in order to have more places to hit and it has really helped. What is amazing is that things are most productive on very hot sunny days as the fish will collect against big rocks, stumps and small brush piles in order to get in to any shade that is available. We will tie up or anchor and flip small slip bobbers out to these locations. A slip bobber gets caught up less. We ill pick up 2 or 3 and move to the next spot. If it is a windy day then you will also catch white crappie with the blacks in windy locations. I think that part of the reason they pick this shallow location is increased oxygen content in the shallow water especially when windy. Normally we notice that this pattern starts when the water temperature reaches around 71 or 72 and will last until water temps fall back down below this level.
You do have a point about the open water. Many many white crappie are caught in summer trolling or drifting the open water chasing shad. Find the shad, find the crappie.
I hope this helps.