In most of the other Yellowstone campgrounds, I would say go for it as they don't adjust for the sites which allow you to let the rear overhang extend beyond the paved site. With hosts permission in Bridge Bay I was allowed to park my 35'FW in a spot designated for 30' trailer but only because the site allowed the trailer to hang over the rear by 6'. so I cleared the road. Had to park my truck next to the trailer and it just cleared the camper door.
However, if I recall correctly, Fishing Bridge has a lot of sites that are basically butt-to-butt which prevents the rear overhang from extending over the rear of the site. This limits most of those sites to actually claimed length.