I never assume that the last brake controller setting is the correct one. Every time I hit the asphalt I lean on the manual lever to check the operation of the trailer brakes and set the controller. This is on every trailer, flatbeds or travel, I own. My empty 6x10 aluminum seems to like a max setting of 3.2V with no boost. Loaded all my trailers seem to like 6.8 to 7.0 volts and boost #1. Never assume that the brakes are clean or that the 6.9 V you used last time is the setting that will work with how your trailer is loaded today. Complacency will get you in trouble when you are towing.
Randy
