Suspect Depth Reading with C120W/DSM30/SS60

[TideRace]

Thank you for the quick and detailed reply.
Differences in beam angle relative to straight down makes sense given the Furuno with the B164 mounted at the greater deadrise angle further forward in the hull is reporting the greater depth. I'm not seeing a feature in the Furuno manual that would allow me to enter a beam angle to get a corrected depth and I'm assuming that there isn't one in the DSM30 either.
Now that I realize that the specified mounting angle range is actually a depth error range, I'll try to remount each transducer to get the beam angles vertical. So much for the nice smooth hull surface.