Our tandem is running 46/30 front and 10-42 rear with GRX di2 and the same BR -RS 785 shifters. I added a RoadLink DM which avoids the need to adjust the B screw to it's limit. Shifting is perfect. And we are often going 2.5 mph on gravel climbs in New England and have never fallen over! So I'd go with option B as well. IMHO 1X on gravel is a compromise with no real gain - but that is an argument for another thread!