Just use simple math. Figure your collar length, then figure where it will end up on your arrow shaft, then install your wraps from that location towards the point. If you want to leave a "Fudge" factor, leave an 1/8" between the collar and wrap.
If your wraps are already installed, place the collar next to the wrapped shaft Mark where it ends, then use a Razorblade to cut the wrap around the circumfence to remove that part of the wrap where you are wanting to install the collar.