Here is good info on where to start looking for crappie as the water temp changes during the season...
Archives - Stuff we don't want to loose.
Your lake may vary some but you are on the right track as looking for the bait...
Your 898c SI has 2 separate SI frequencies...(see depiction below)...
While the 800kHz is going to give better detailed images.. The 455kHz should not be overlooked as it will show fish higher in the water column out to the sides...
As fall crappie are basically looking to fatten up for the winter..they may be moving a lot chasing bait up in the water column giving the 455kHz (180degree coverage) an advantage of detecting those moving fish...
Keep moving and find the bait...and give the 455kHz SI beam a try...
Rickie