The only instance I would ever select 200 OR 83 is if I wanted to pinpoint a piece of structure to be in the 200kHz 20 degree cone ... If the setting is at 200 and a brushpile shows on the screen.. You can be certain that brushpile in nearly "directly" under the xducer..:

A 20 degree cone is a very small cone...(something like 1/3 of your depth)..

Rickie