Thats the rear wiper arm that requires some trimming, but some people has swapped it and it's fitted fine, others including me have had to sand paper the cap down so that it won't pop up when it does a full wipe.

It varies from car to car - I bought mine from another Ibiza owner who had already sanded his down to fit and I had to take loads off the bottom of the cap, the inside of the slit where the nozzle points and the bottom of the arm where it was scraping the screen at one point.

I think it depends how high the mounting bolt has been set