Different brake pads could be a solution as well, though 180mm on the back is not a bad idea. I have 203 mm on the back of our bullitt with jagwire breakpads
I have 220mm floating rotor on the front of my GSD with magura MT5 and 180mm on the rear. When the 180 wears out, I have the adapter and rotor ready to go up to 203.
This is the way to go, biggest you can fit IMO. It should be illegal to spec a 160 rotor on cargo bikes front or rear.