FWIW: I have a Furuno 667 ( older unit ) - Drum so up on my finder almost like a triangle shape - roughly 1-2 feet high but on bottom.
If you zig zag along the Stone Rock area on a calm morning - you'll see the bottom is mostly flat - small humps / gullies.
When you see some thing odd - worth dropping a bait on it.
It also pays to either zoom in / bottom lock or adjust setting to get the most screen. You do not want the screen on 50 feet when in 20 feet. You lose more then half the view area.