The sizeL or sizeP don't stretch the thing they "hold". So, if you have, let's say, an image 100x100 and you say size=50;50, it will show just the 50;50 of the 100;100 (1 fourth) of that image. By the same account, if you say size=200x200 to an 100x100 image, it will show all the image, but the image will have a span of 200x200. What I mean by that?
If, for instance, you apply the size alias to a button like the media buttons, like, pos=0,0 and size=800x480, but the button size is only 100x100 this will happen:
1)The picture will be shown at the position 0,0 spanning 100 to left and 100 to bottom (as expected, it will be in the top left);
2)Because of the size chosen, the ENTIRE screen will react as that button (of course, this may not be true unless this is the first widget drawn, because all the other widgets would have a preference over that one, but if it is the last, the entire screen will be just a big button, nothing else would be able to react).

I hope I was able to make it clear |:)