With my sharpest lenses I love the results of HP5+ at 11x14" (actual image size less than 11x14" obviously due to the easel blades). Souped in DD-X the prints show almost no grain at that size when exposed and developed correctly. Surprisingly good.
I do wear eyeglasses. I didn't think to try without them.
I too find I can focus very well without the magnifier though I guess I don't trust myself that well yet. I also wondered if I should focus differently for RC or DW fiber since the paper thickness is different. So far I've used the correct dummy paper in the easel, refocusing when I switch but perhaps I'm being silly.
Doing two test prints is of course the obvious answer though if I'm really just confused by diffraction patterns then it would be a waste of paper, though not much more than my usual printing workflow LOL