here, I did for you.
1 foot of 18 AWG is .0063 ohms so the drop with one amp is 6.3mV
1 foot of 22 AWG is .016 ohms so the drop with 1 amp is 16mV

So at max balance current the different would be about 10 mV. At 300mA balance current, the drop difference is only about 3 mV. So as the balance current ramps down, the difference is very small.