It's an autopilot mode,, I'm comfortable with flying without GPS as far as piloting goes,,, Fly several types of models and quads. Not sure how that applies to Watch me ?
It's fair enough but even in auto pilot modes, if you want to set it up, there are safer distances and moves that I would personally suggest for someone that I would feel comfortable with that could take control if need be and also tweak any suggestion I would make.
When you say "no elevation changes" you just mean what elevation you're at, you don't want to change from at all.
If I were you, I would just get there early and find out (would be great if someone was there to do a test run with the car at full speed) and then find out what the lowest height would be from whatever point you want to catch all the action. From the center, behind the cars, other side of the track?
All these variables will determine how high you need to be in order to use the watch me funcunality to its fullest.
Personally I would just stay about 50' feet high and then just figure out a good distance based on the behavior of the car and maybe try a CCC around the track and then the only thing I need to worry about is the camera.
If that wouldn't work and who knows with CCC, I would try the same thing but manually just control the camera from whatever distance feels right after a test. For me, it's sort of hard to imagine what the right distance would be because I've never shot a race track.
I have done orbital shots around people riding horses though and because I don't want to spook the horses even though the guys from this ranch swore I couldn't, I grew up with horses and know for sure any horse could get spooked by my then P4, but I did that all manually and it was a hard shot so and I'm telling you this because the shot you're describing is so simple that I don't really know how to give advice on it, at the risk of sounding rude. Not trying to be, just honest.
So I guess that's the long way of saying not sure. I would have to be there to give you my real exact offerings of height and distance but that's the method I would use is do a couple test runs and the right distances on both will be obvious. Anyone that just tells you is only guessing based on their experience but every place, the wind, the speed of the car, etc is all gonna be variable even with each car not going faster than 22mph.
If it's one car, figuring this out should take about 3 minutes.