As an amateur radio operator (ham), I'm virtually positive the culprit is not the SWR of your antenna. In any case, the CB antenna supplied by Honda is sealed and cannot easily be optimized for SWR. I've tuned numerous CB antennas in my chapter on pre-2018 bikes with no discernible difference to reception by other bikes. The owners like everything about their bikes to be "perfect", so I play the game.
Unfortunately, I do not yet have a 2018/2019. But, it sounds like you're overmodulating. On my 2003, overmodulation happens when I increase the volume (gain) of the intercom too high. It turns out audio from the intercom is tapped for the CB on pre-2018 bikes. If you can find a way to adjust the modulation of your Bluetooth connection to the bike, try lowering it (ie, decrease the gain), and your CB transmissions will be much clearer.
The above applies to when you transmit. For receiving, the solution is more difficult. The same problem was reported by many riders of the pre-2018 GL1800's. What appears to be happening is that other riders in close proximity are transmitting at too high a power and are "desensing" the front end of the CB receiver on your bike. That's the term we use in ham radio when someone else is transmitting so close to me at a high power that I can't hear anything. You can try backing off from your group - give them some distance. Other than that, you need to decrease the gain of your antenna, which, ironically, can be done by detuning the antenna and increasing its SWR. However, that's difficult to do with a sealed antenna. If you're willing to experiment, adding a splitter to the transmission line between the antenna and CB should decrease the received power (and transmit power) by half. If you follow this route, be sure to terminate the unused terminal on the splitter with a 50 ohm load.
Arthur
VA3BIT
