Well the station itself doesn’t care how big or small the tips are, it only cares about the elment/TC, so if it “sees” the 8 ohm element/TC you’ll get heat at the tips, if they all measure approx 8 ohm then, the temp at the tip is going to be very approximately the same, of course this could still == 100C variation between tips until after calibration but they should all get hot.
I use the aluminium handle variant and it uses a very different prong style within, which imo is much higher quality than the other versions, so I would be checking the voltage on the points of the tip directly (+ and -) while it’s slid into the PCB/prong adapter and seeing that you measure a consistent voltage.
I’d check the thermistor also, (10K i think) on the handles board, might also be worth switching that to the “CPU” NTC in the menu and if it resolves the problem then you can blame that.
I doubt this is your problem, theyr’e just a thermocouple, nothing special, your MM K-type likely agrees with it right?