3% loss from the panels to controller I suppose is acceptable as the voltage is between 17 and 20 volts for a 12 volt nominal panel, losing some volts can save some money in the applied wire size and the controller still gets plenty to output the 13 to 16 volts demanded of it. I recommend 2% or less between the panels and controller. Where loss is critical is between the controller and battery(ies). The controller is configured to provide a specified charge required by the batteries, usually 14.1 to 14.9 volts for bulk/absorption, depending on the batteries. 3% loss of voltage between the controller and batteries is unacceptable. Properly charging batteries is facilitated by providing for virtually no loss between the controller and the batteries. That's why the controller should be close to the batteries and the wire used should be at least as big around as one of your fingers. JMHO
