I usually do them up to 4nm using a torque wrench. When I asked prime (who make my bars) they said that sounds too little and to use the torque recommended by the shifter’s manufacturer. Which for sram is 6-8 nm. That sounds very high imo for carbon bars
given they don’t shift at 4nm, is there any reason to do them up tighter?
Maybe use a bit of carbon paste for extra grip. My latest gravel bike came with a bit of grip tape attached to the bars under the sti's
If they don’t slip then they’re tight enough.
When I queried brifter torque for my EC70 AX bars, Easton suggested just enough to stop them moving in 'normal' use. I think though that this was to protect the brifters & allow them to rotate if taking a hard impact, rather than protecting the carbon bars.