Some of the other Regions are enforcing the broomstick rule with Boxsters and Cabs - even though their rules cite the National "factory protection" paragraph, and some require an additional 2" clearance between the broomstick and helmet. Good luck with that, even with a Brey-Krause extender...
My suspicion is that some of the other clubs have rules which may be similar to PCA/SDR, but they just don't enforce them as rigorously, which makes everyone think they have less restrictive rules. That will work right up until the first major incident, when their insurance company rejects a claim for failure to comply with the safety rules.