OK, let's step back a second.
320mv is not significant... please, too many get hung up on such MINUTIA, really, it is almost nitpicking and really serves little purpose. Even perfect matched cells wobble voltage wise at the top. All LFP will settle from 3.65 down a bit while they rest, often unevenly making one or two cells standout, not unusual. A reminder, that these cells are Within the Grade-A Spec of the manufacturer but thee are not Voltage & IR Matched and batched cells and so such deviations is not unusual. This is one reason the Top & Bottom Balancing is mentioned so often.
Assume a generalized rule of 1mv per amp hour capacity is not unusual. Often a Passive balancer (which burns off hi volts only from hi cells) can address such small deviation but Passive is very slow. Larger Capacity cells are often too big for passive to be efficient due to it's slow process.
Longevity practices dictate that we stop the cells at 10% from bottom & 10% from top providing 80% of their capacity for use. 2.75 & 3.28 respectively per cell.
Here is some Excellent Information from Orion BMS Folks (a pretty darn credible BMS Company who knows their stuff. The BMS specific stuff is moot as it depends on what your BMS is, but the battery info is what we want anyway.
High Resistance Cells : Again Orion hs some helpful info.
Something from Battery U:
Learn about battery technology, battery maintenance and battery life at Battery University
batteryuniversity.com
Hope the info helps.