Piston 3 Carbon Buildup

Decided to perform a maintenance spark plug check on my 2015 2.4L Dart. While changing the spark plugs, I noticed that the threads on plugs 3 and 4 had some carbon buildup. Decided to take a peek down each cylinder, and cylinders 1, 2, and 4 all had normal piston carbon deposits for an 80k-mile engine. However, on piston 3, there seemed to be significant buildup (couldn't see the shiny surface of the piston). When I first got the Dart at 75k miles, I performed an oil change with BG EPR...

Piston 3 Carbon Buildup