To use the sync ID, you set it in the layers window. Set the ID on the bottom of the layer to you want to sync to. So let's say you use sync ID 1. You would put that on the layer you have your loop on. Then the longer file set the play mode to sync to ID 1. It should loop around at the exact same time as the loop. Then make a cue, or preset to cross fade to the layer that is not the loop and change play mode to play once forward or whatever you need to do. It should transition and play past the "loop point"
If you are set to blend glitch C you shouldn't see anything happen when you crossfade. Or if the loop is on a higher layer and the longer file is on a lower layer, run them both at full and bring down the loop, again, shouldn't notice anything happen.
Good luck