You should use R-mode it helps a good bit. You should be able to get your wattage from the 90s range to at least the 80s or high 70s in the software reading.
Even though all of your cards are the same model, it’s probably just 1 or 2 of them that don’t like the exact same undervolts as the others.
I’d lower the core voltage some, lower/raise the memory voltage slightly, and use the SoC frequency and voltage values, something like 960mhz/860mhz or try starting with 960mhz/960mV for stability. Though with R-mode you can go even lower on the core.
See the post above of mine running 46.3mh/s at 68 watts. You’ll just need to find which specific card doesn’t undervolt as well and keep it stable while keeping the others lower.
Nice rig though haha I love these cards.