The in balance is not much.......just a few %..........say right bank at 12.7 the left would be 12.8-9 at "wot"
So best practice is to tune to the lean bank and run a little rich on the right.
There are ways to fix this lean bank but 99% of cars it is not worth it.
This in balance comes from the back cylinder on the left bank running a bit hotter (why?? position, water flow, design??) ....if you are serious look at the EGT on each cylinder.