I believe any/all changes in current flow and/or weather conditions, prompt crappie (and most other game fish) to modify their normal activity level. Up or down. It's our job to figure out which it is at any given time. There are no "rules" when it comes to fishing. Just as there is no best presentation. It's all about trial & error and for an angler to be open minded enough to keep trying different things, to narrow down the "rules" of the day.
"A voyage in search of knowledge need never abandon the spirit of adventure."