do they measure from the middlefinger tip to middle finger finger tip, or middle knuckle to middle knuckle of a clenched fist? It is amazing to see Sean spencer, at 5'10, having a longer reach than 6'2 Tito Ortiz. Or Conor having a longer reach than rampage.
Why? Turning your torso in punches makes your punches longer. Thus the torso width is important when discussing reach. Wingspan also gives an indicator on frame size as well. Someone taller and with a longer reach will have a bigger frame in general than someone smaller.
Not always though. Im 6"2 76 inch reach fought at lw could make fw if i did a ufc level cut. But generally you are right like the guy i mentioned above.