if the wiper parks correctly at bottom of stroke I would not alter the position of wiper. If the wiper goes further than it should at bottom of the screen on wipe then you can remove the nut holding the wiper arm, prise off arm gently and reposition further around on splines. You could do this even if the wiper does not go to far at end of stroke and split the difference of the area not being wiped so that you have some unwiped area at both ends of the stroke.
The wiper mechanisms on these car are prone to rusting up of the spindle shafts. I would firstly try spraying some WD 40 into the spindle shafts over a few days and give the wipers a try after each spraying. If this does not work you will have to remove wiper mechanism and gently remove shaft from spindle case/ clean off any rust and re assemble with some copper grease. I did the strip down on my first Alhambra and it lasted for the next 6 years.
