I dont know what suspension you're runnnig or plan on running, but i had H&R coils which were spun pretty low. I hit a few issues here and there, but nothing too serious that made me want to raise it.
About the "T" shaped piece you're talking about...honestly i dont remember seeing that. Nothing on the skirt went as high as the door sill though. Everything stayed below it, so my guess is that its just there to possibly make a more snug fit between the skirt and the body of the car?...not sure though. If you have a pic of it, post it up.