FAA require one of the points to be 250NM in a straight line from one of the others. I'm currently planning a potential candidate for mine at the moment. The advice in the aero-experience document on their website is poorly worded but I read it as requiring an A-B-C flight with A-B, B-C, or (most likely) A-C being greater than 250NM. I'm thinking KCHD to KSAN with an intermediate stop.
Is the 300NM distance measured as the sum of A-B and B-C straight line distance or the route as flown?