That's a helluva tool. All I've ever used was 2" schedule 80 pvc pipe.
Not a body shop owner, we need Bill Gaino for that. However I've rolled a few fenders in my time.
Agree with Rick, be patient, just go slow, roll the fender in small increments.
Roll both front fenders from about 10:00 to 2:00.
The rear fenders taper towards the back however. So I'd roll the left rear from 10:00 to the belt line behind the tire (about 3:00), and I'd roll the right rear from 2:00 to the beltline behind the tire (9:00). This was necessary on 6018 when I installed the 325/25R20 rear tires. I'm not saying this is necessary for your installation (I don't know) but since you have the tool, why not?