I did a few more flights to compare different antennas, and also the "long range, slow" setting.
This time I used a waypoint mission to have the same course in each flight. The furthest point of the mission was 2.5km from the home point.

"Short antenna" is the one I used in the first video. "Long antenna" is this one.
The long antenna was mounted vertically (perpendicular to the wing surface).

The blue dot is the home point, the red dot is 2.5km away. All flights were done within about one hour.

Interestingly all configurations were receiving some packets at the 2.5km point. I think that location might have been just a happy coincidence for some of them, because there were marked differences in reception along the rest of the course. So far the type of antenna used has had more effect on the outcome than the modem config, so I think it would require longer distances than this before the "long distance" setting shows its strength.

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"Medium range", short antennas at both ends (same as in first video)



"Medium range", long antenna on ground, short antenna on plane
Not as good as the two shorts together.



"Medium range", long antennas at both ends



"Long range" (Bw125Cr48Sf4096), long antennas at both ends
This one takes four seconds per packet to transmit, so there are far fewer points making up the line here.