After more research, I can see that it's the cone angle that matters, not the frequency of the transducer. Most the HB head units operate at 83/200 kHz & so far it looks like 200 kHz is synonymous with a 20 degree cone angle (for HB.) Moving to Garmin, however, that relationship changes. The bottom end "Garmin echo 100" operates on a single frequency (200 kHz), but the bundled transducer has a 60 degree cone angle! If the head unit also causes the US2 transducer to cover a 60 degree angle, this would cause cross talk as shallow as 10'.