I have just taken my showerscreen off to have a look and, as lawrence says, the flow is uniform all around the outside of the dispersion disk. There may be a little water from the centre of the disk but I could not see any. On mine it does not spray out but rather forms a circular curtain of water.
I guess there could be an obstruction in the drilled hole supplying the water to the dispersion disk but I think it is unlikely as you descale it regularly. If it was obstructed you should see it spraying out without the dispersion disk in place.
As the dispersion plate is clean and crudless I guess it is or was fitted slightly off centre. Unless it is spraying from one side I would not expect that to cause a major problem. If it is of concern to you perhaps you could let the machine cool down to avoid scalding and then play with a cocktail stick in the side with the least flow to see if you can centre the disk better. If so then a little force in that direction may centre it without the cocktail stick.
Edit: I have just seen your latest post whilst I was composing mine. It sounds as though your problem is solved.