If you look at this picture you can actually see the front welded channel is longer. I have sold rear channels to people who have grafted them on as they are often rotted or missing. You are correct on the "T" channel it fits in the slot and the other side acts like a wiper on the glass. They can be a pain to fit in but there is a cut area to feed 1/2 one way and 1/2 the other I used liberal amounts of KY on mine. I gave up on the clips and screwed mine in as you described earlier in five places.
https://www.flickr.com/photos/advance-design_parts_co/14184302391/in/set-72157631868452754