That is a good find. And it shouldn't be surprising.
If the frame rate we set not only sets the rate at which frames are compressed and streamed, but also sets the rate at which frames are captured by the camera and thus available to the camera's "brain" for use in performing tracking, then it should be no surprise that a higher frame rate should allow the camera's tracking to work better and more smoothly.
For a PTZ camera with autotracking, it would be nice if the camera could operate at its fastest frame rate for the purposes of analyzing targets for the autotracking, BUT also allow the user to set a separate frame rate for the purposes of compressing and transmitting the video over the Ethernet connection. That frame rate would need to be an integral factor of the main frame rate, of course, but that would likely be just fine.
So, for example, the camera could sample at 60 frames per second, and use all of that information for autotracking. But then you could select, 5, 6, 10, 12, 15, etc. FPS to be compressed and sent out the ethernet connection.
Of course, one fly in the ointment for this would be that you would always have a maximum frame rate imposed by using long shutter speeds. You obviously can't shoot 60 FPS if you're using a shutter speed of, say, 1/30th of a second. So you'd have to (as usual) make some tradeoffs when selecting the "real" and "transmitted" frame rates.