I find Stubben bridles a bit of an odd size to be honest. Our 12.2hh pony has a Cob size which fits well but the noseband is small in comparison. A 16.3hh of mine also has a Stubben bridle, his is size Full and once again it fits well but the noseband is too small in relation to the rest of the bridle.
Agree about the proportionately smaller noseband. They often sit oddly too, or the flashes on two of mine did, twisting to the same side no matter that they were correctly fitted to the horses.
My local tack shop sold me one, having fitted for a saddle for my 17hh t.b full size. I took it back the next day as it was miles too small and the cheeky sods would exchange or refund!! knowning I had bought a saddle that day.