Your own linked calculator says it right there!
Allowable voltage drop 3%:
View attachment 67122
View attachment 67123
Now, average discharge V on LifePo4 cells is 3.2 V.
Vdisch-pt 3.2 V * 4 = 12.8 V
If you would use 12.8 instead of 12.0 volts, amps and resistance on wire would be even lower.
I have been working on electronics ever since I made my masters in Electronic Engineering back in the 90s, incl on such things like S-76s.
Really love Will's YT channel and his inspiration, but this forum is full with a bunch of hobbyists trying to tell people what to do. I think I'm done here for good.