This is why I think they should just set a maximum service height (e.g. 1.3m or whatever reasonable height) to remove variations. Then, there could be a white tape on the net marking this height. The service judge then sits on a height adjustable chair/stool, so that their eyes are precisely at this level. By comparing the shuttle to the white marks, any serve with the shuttle higher than this mark is called a fault. If someone has a better idea, then fine. But in any case, BWF needs to do a better job on this. How much controversy do they need before changing the current service rule?