Picture it. You have a rock that's not 100% flat and you want to mount a perfectly flat substrate to it. If you tighten all the corners down, it' will be snug, but most likely bent, since it wasn't' 100% flat. If you only tighten it til it almost bends, it won't be secured properly. Now it can blow off, be knocked off or just palin stolen. What's your choice ??