Elbert - I have just gone to the DAN Americas website to try to find the latest recommendations on flying after diving. I was unable to find a succinct statement of recommendations, so I scanned all likely looking articles. The only one I could find that gave a minimum altitude was this one. You'll see that it refers to a minimum altitude of 2000ft - my memory is of 3000ft. Either is above the heights I mentioned. But if have documentary evidence of a lower recommended height I'd obviously like to see it:-

Provisional Flying After Diving Guidelines
The following recommendations, which apply to recreational divers, represent the consensus reached by attendees at the 2002 Flying After Diving Workshop. The recommendations are based on earlier published work and recent experimental trials as described in the Workshop Proceedings. They apply to air dives followed by flights at cabin altitudes of 2,000 to 8,000 feet (610 to 2,438 meters) for divers who do not have symptoms of decompression sickness (DCS). The consensus recommendations should reduce DCS risk during flying after diving but do not guarantee avoidance of DCS. Preflight surface intervals longer than the recommendations will reduce DCS risk further.