DB
Splashing those in singles will only work well if you are trying to draw them to a LARGER area....if you know how the Crappie move around your lake between spawning, feeding, and suspending areas, you can control their movement by placing singles they can follow between areas, and then installing a large groups in their favorite areas....then they will move along these areas to feed etc...and it will continually draw in new fish!
It really helps to vary your cover so the areas can hold minnows/baitfish, craws, small organisms, and so you have a complete ecosystem.....then you get the best BANG for your $$ and time!