The problem is Shang Kun is a lefty FH attack oriented player, playing rigt handed guys, most of the issues with illegal serves come from opposed hand players, it's the same with Lebesson as he's a lefty playing most of the time... right handed players, the scope of vision is then narrower than for a player able to see a serve from a more opened view, say in diagonal. And that's also why umpires and assistant referees are not the right persons to judge the validity of a serve, simply because they are not standing at the same place as the receiver.
That's why the law saying " it shall not be hidden from the receiver by the server or his or her doubles partner or by anything they wear or carry" is sometimes meaningless and stupid cos' it depends on... where the receiver, or receiver partner's, stands.
When camouflage was allowed, nobody was whinning that much, when speed glues and boosters were allowed, nobody was whinning or complaining such as Mizutani did.
Bring back the old era please...