As a general rule of thumb, we would advise against using player aircraft as AI traffic, as these aircraft have not been optimised to be used as AI traffic and therefore can cause significant FPS/performance issues if several of them are loaded into the simulator at any one time.
If you would still like to use the aircraft as Ai Traffic, then unfortunately, the Wingspan Options setting in the Traffic Control Centre will not have any effect on the wingspan of the aircraft, as this only controls the wingspan value of the Ai models that are included with FS Traffic. You could change the "wing_span" value manually in the flight_model.cfg file of the aircraft you wish to use, but please note as this is a player aircraft, any changes that are made to the flight_model.cfg will also affect the handling qualities of the aircraft the next time you fly it as a player aircraft.
Mark - Just Flight