In my case, moving the wipers on the spindles just caused them to foul the body. Stripping the motor contacts and cleaning them made no difference.
If the arms go to the correct position you would expect them to park in, but then run on longer and raise up a few cm, it is worth cleaning or changing the wiper relay. It gradually wears, furs up with contact dust and becomes sticky running longer than it should on each cycle. This can only be a fraction of a second, but long enough to give the characteristic 'early z4 wipers too high' look.
It is blue and located on the back of the fuse panel behind the glove box. Available from the dealer for about £20, the updated part was green.
I removed everything for access to change mine but having done it, I believe it would have been possible with access from below and a torch/mirror.
Picture of my old relay, innards and location attached hopefully.
I was sceptical this change would solve the problem at first, but with the new relay in - perfect parking first cycle.
Euan