I have an old Humminbird that I rigged for my canoe. Before the days of dual transducers. I had two different Cone Angles. One wide angle for coverage, then switched to a narrow beam for precision. I'd dig it out but I have a 385ci.
But I can see one transducer for for location and a second on the trolling motor for pinpoint fishing. Or as you said, two different holes 20 ft apart.
The switch, by the way, worked great.
Mike