It's always best to make the controller to battery wire run with as large a wire and shortest distance as possible. However, for what you describe it will make very little difference for essentially a system being used primarily as a battery maintainer. Also with the ProStar you have ability to run battery sense wires which will make up the difference for slight voltage loss on the battery cables as the ProStar will controll voltage off those sense wires and raise charge voltage to compensate for the charge wires loss. I also use a ProStar controller
