That's a good point and gave me an idea on saving some time (which is where you were going with this I'm guessing). Comments I've seen says 40 degrees (PING says "narrow beam angle" in their spec, but I found a number in another question in this forum). I can break up the initial 180 degrees into 5 sectors as a quick first-pass to narrow the search range to a 40 degree quadrant. Then I could disect that 40 degree quadrant into 5 degree chunks (or whatever the MIN_ANGLE_DELTA ends up being). That would cut the number of scans down to 13 scans instead of 36. Thanks for that idea 
Unfortunately, that's still a 9+ second scan cycle 