I think i've seen trace velo on YT use a bit of plastic wrap around the area to increase friction? i'd have thought the max torque would be dictated by the bars, because that's what is at risk of cracking. 6-7nm sounds right. 10-12 sounds very high indeed. on carbon bars, i'd be afraid to tighten that much. obviously on alu, you don't care.
I took it apart and put some gorilla tape under the bands of the shifters. It is better but still needed 8Nm to keep it from moving easily. My guess is if I try hard enough, they will still move by hand. Took the bike for a short ride and they didn't move from tucking at them on climbs.
Got a lot of thoughts on my experience installing the groupset, setting everything, fine-tuning, ergonomics, shifting performance, etc. For now, the most important thing is the shifting is beyond my expectations for what I paid for it ($618 CDN).