I have found it not uncommon that equipment has been designed to not allow the whole frame to be printed. Sometimes one needs to do little modifications to align things, even with 'pro' darkroom equipment.
Some examples I have encountered, my Phillips 35mm enlarger. With the glass carrier and adjustable masking blades and a common six-element lens. If the blades were just a millimeter or two off the image would go outside the sharp image circle. Solution, use High Magnification (big image circle) lens with this enlarger (lens cost ten times the cost of the enlarger.) Another example, the Schneider Betavaron zoom enlarging lens. It does not cover an entire 35mm full frame negative. Another example, even my late model Durst 10x10 enlarger has only a millimeter or so clearance on each side when trying to projection print an 8x10 negative and include the rebate.
The old darkroom worker's advice of always using an enlarger 'one size bigger' is often good advice.