ah ha Loadswine told me about your
problem.... hmmm and I'm glad other than that you Leon owners are finding my method of using the Golf IV speaker adapter kit with leads a god send for changing the speakers. I just came about it via a bit of risk taking since I knew I needed a speaker adaptor kit and saw that my speaker size would fit the Golf IV kit and thought... oh well they might fit the Altea being the same VW group. The hack saw did the job of dropping the adapter back into place. All the holes are in the right place etc.
Think I know what you mean by cutting it in half, slicing the tube down so it's not so long. You need power tools

.... assume that everything else will line up OK and you won't loose something that you need by cutting.
Simon34 you needed speakers with tweaters in them and dump the Seat ones since if they are like the Altea ones which they will be they are rubbish and not mounted in the right place....
I still think that the Infinity ones give you an amazing sound off the headend and that's been after 18 months now. The base sort of ports into the car door.