He can’t tell you anything. He’s not a machinist. He plays one on here.
I’ve used that fixture many times and you are correct. Even when you spend forever dialing the fixture in you still can’t move the bores very much if at all.
We used it mostly to make .842 bores .875 for the Chevy guys and it’s fine for that. It’s actually not bad for 98% of the stuff out there.