I have had a CGFXII-160 for more than ten years and haven't had any problems using the entire width.
Load the material, set pinch rollers in position, tell the cutter to read the position for two, three or all four rollers and it is ready to cut to that width.
What program/plugin are you using to cut?
I use Mimaki FineCut 9 as a plugin from CorelDRAW 2020, and it works great.