HoagieTime

I have a 2016 wagon 2.5 lwb with 21k on it that i recently picked up lightly used. I've been getting about 16.5 city, and 17.1 mixed. I normally only haul my lunch to work but occasionally fold the seats down for tools and put lumber on the aluminum aero bar roof rack for short trips. I noticed the disappointing mpg so I've been driving in a way to maximize my fuel economy, easy on the gas and brake pedals. I still have time on the factory warranty so I'd like to bring it to a dealership to have them looking into the cause, though I'd like to have some clues as to why such low mpg first. Tire pressure is as mfg spec, and I don't let it idol or warm it up. The longest its running while stopped is on long stop lights. Driving in normal drive mode not sport, and set for anticipation mode. No codes are showing up, says systems are normal. I also weigh 150lbs so you can rule out excessive human cargo.