I designed the Matrix TR Arena. On the Matrix buggy, you must use the top hole in the tower for maximum uptravel. On the TR Arena, you must use the lower hole for maximum down travel unless you use the long shock ends. I have never tried the long shock ends, I have always used the short ends front & rear. The CVD's on the production truck were made a little too short, so to prevent them from poping out you must use the inner hole on the arm and the lower hole on the tower when using the short shock ends.
Now if you want to raise the center of gravity (and get some extra down travel), you can use the long shock ends on the front & rear and use any of the shock mount holes in the arms and towers without any problem. The RTR's come with the long shock ends on the rear already to keep it simple but the fronts pop out sometimes also, so they should come with the long ends as well. But for racers, we want the best performance, maximum uptravel is the best for handling, as long as you use the right holes to keep them from poping out. I have been told that they are going to make new longer CVD's, but that will take some time.
I poped out a rear CVD the 1st jump I hit the day I got the production truck. I changed to the holes I recommend right then, and I have never poped one out in 7 months of racing since then.