I produced this video in 2017. In the video I mention that my favorite version is the flat double overhand. I quote some testing done by Grant Prattley in New Zealand. I did not mention in the video, but I knew at the time that the guys at Rigging for Rescue in Ouray Colorado had also tested it.
Recently someone posted a comment on the video on my YouTube channel pointing out that Grant did more testing in 2020 to see how some versions performed with ropes of different diameter.
Grant’s tests showed the result is different when tying what he referred to as 10mm on 9mm vs 9mm on 10mm. One is recommended and the other is not. I am not going to try to figure out which is which. And I am not going to stop using the double overhand. I have used it with 9.5mm and 8mm combos with no problems.
BUT … Having said that, please refer to the video from 0:50 to 2:30 for what I consider the only proper way to use any of these “flat” (or offset) bends.