Shortly after I posted this I discovered the solution. A bit strange since I have been looking for it for days.
This was the problem;
$ sudo DISPLAY=:0 XAUTHORITY=/var/run/lightdm/root/:0 nvidia-settings -a [gpu:2]/GPUMemoryTransferRateOffset[
3]=500
This command adds 500 mhz to the memory speed - in Performance level 3. It seems my cards are operating in Performance level 4 and this did the trick;
$ sudo DISPLAY=:0 XAUTHORITY=/var/run/lightdm/root/:0 nvidia-settings -a [gpu:2]/GPUMemoryTransferRateOffset[
4]=500
I wasn't even aware P.L 4 existed, but apparently it does.
This is the situation right now, up from 52MH/s - not too bad;
20210121 23:40:40 GPU #0: RTX 3060 Ti - 60.10 MH/s, [T:63C, P:129W, F:42%, E:466kH/W], 1283/1283 R:0%
20210121 23:40:40 GPU #1: RTX 3060 Ti - 60.10 MH/s, [T:58C, P:129W, F:30%, E:466kH/W], 1281/1281 R:0%
20210121 23:40:40 GPU #2: RTX 3060 Ti - 62.06 MH/s, [T:58C, P:129W, F:30%, E:481kH/W], 1283/1285 R:0.16%
Ps, the 2 rejected shares on GPU #2 came in at higher clock speed (64 MH/s) so I eased up a bit.