I have tri-power and an O2 gauge as well. My warm idle AFR is 13.5- 14.25. I cruise at 13 - 13.5. WOT is 12.5 - 13. The gauge can bounce around a lot.
If I had 10, that would be a problem. I don't see what you have as a problem. Maybe you could down jet one more size on the center carbs or adjust that power piston spring.
It is better to run a little rich vs. a little lean I hear. Also, from:
https://www.safrtool.com/SAFR-AFR-values.asp
6 AFR - Rich Burn Limit (engine fully warm)
9 AFR - Black Smoke | Low Power
11.5 AFR - Best Rich Torque at Wide Open Throttle (WOT)
12.2 AFR - Safe Best Power at Wide Open Throttle (WOT)
13.3 AFR - Lean Best Torque
14.6 AFR - Stoichimometirc Air/Fuel Ratio Value (Stoich)
15.5 AFR - Lean Cruise
16.5 AFR - Usual Best Economy
18 AFR - Carbureted Lean Burn Limit
22+ AFR - EEC / EFI Lean Burn Limit