I'll throw my tuppence in, for what it's worth. I'd be a little skeptical of a cal course that short, just because of the possibility of a single wobble, bump or whatever throwing the results off.
Granted, this is probably what they said back when cal courses were a half-mile or more. But I still see the possibility of a small error being carried over, that would be "smoothed out" with a 300-meter course.
Take that for what it's worth. Y'all know more about riding cals than I do.