I agree with jpsdad about deeper brush as the best way to concentrate crappie for fishing.
We knew of two large brushpiles in 20' water of a 400-acre private lake when we were kids. We used to compete on how many consecutive casts you could throw a small jig and land a crappie. For some springs, the winner would be over a dozen in a row.
In both cases the deep brushpile came up to within 5-6' of the surface.
We would occasionally catch crappie off of weed beds or timber along the shoreline, but we mostly caught bass out of the shoreline cover.
Despite the lake being an excellent multi-species fishery, the crappie population would definitely exhibit strong cyclical behavior.
Some years we would catch over 150 crappie that were 4-5" in size with maybe three or four crappie over 10". The lake manager told us to keep all of the little ones to cull them. Then a few years later we would catch fewer crappie, but lots of nice fat ones over 10". The manager would let us keep 5 each of those, and they were very tasty fried up!
I have seen similar results in watershed lakes of 10-50 acres, where we caught lots of bass along the shoreline structure, but caught almost 100% of our crappie on brushpiles in the deeper water near the dam.
I don't know what controlled the crappie recruitment in those situations?
However, I do recommend you establishing some deeper water brushpiles to give you a more reliable method of SAMPLING your crappie population. That should help your management at least a little bit to get some more data points.
P.S. I have caught crappie over "fluffy" brushpiles that were made by cabling cedar trees together. I have also caught them over brushpiles that were created with large tree trunks and essentially zero fluffy component. Something about the cover in an otherwise pelagic environment has always been the best crappie concentrator in my limited experience.
