Mmm, funny should say that. My bender is a toy one from Toolstation, no adjustment required.
On my toy for 22mm the roller is 40mm from bottom of form, thinnest part of die is 18mm, no adjustment so this looks like a plan.
This hired one looks like a Record 35, i've set the end hook so tube is level in the form, i've set the roller so clearance from bottom of form to roller is 44 mm (thinnest point of die is 16mm, tube is 28mm). Is that anywhere near? (Had a good search on here and Youtube for setup clues, no joy. No guide marks on the side of the roller carriage, Jewson instruction sheet says put the right size form & die in and bend away. Ta
I take it that you are pulling the bends up and not downwards, put the hook/stop in the third hole down for 28mm, (the first one's for 15mm) slide the pipe in, it should be running down away from the back of the bender, slide the guide in and rotate the handle until the wheel bites on the guide but not too tight, then pull away.