Came up with a couple of answers to my question the other day. Set up the D-RTK 2 base station on a river terrace. During the first flight I was 850' upstream and about 20' lower than the base station with a line of a few large spruce trees in between and the base station just visible in the distance between a couple of the trees. Worked just fine. For the second flight I was 650' downstream and about 40' below the base station with several spruce trees in between. I couldn't see the base station at all due to trees and, maybe more importantly, I was below the line of sight below the edge of the bluff. Again, worked fine. I think the second setup was more telling since radio communications are sometimes difficult when one of the radios is lower than the other and below the edge of the bluff. I've had radio communication problems like that when surveying with a robotic total station with the total station up on a terrace and me, with the data collector, along the river just below the line of sight (with survey rod 8' tall and still visible to the TS). Thought the DJI remote controller and D-RTK 2 base station might run into similar issues but, instead, worked great.