maybe y'all are just a lot faster than me. The 3 x 20 minutes would be about 3 x 2.5 miles for me. Sure, it wouldn't be easy, but it's not so far beyond the 6 that most people are saying, and it includes breaks. *shrug*
PRs:
5k - 22:53 (May 2015)
10k - 50:00 (unofficial; part of 20k race, March 2015); 50:33 (official; July 2016)
HM - 1:48:40 (Apr. 2015)
I don't really train at half marathon pace so I wouldn't run 6 miles at it either. I use the old school method; faster intervals done at slightly higher than normal mileage.