Hey, I'm meticulous about proper mounting of the reed, particularly in how it relates to the tip rail. I like it pretty much even with it or just a hair under - but never over. I also need reading glasses but never take them to a gig. Still, I'm pretty good at getting the reed on right. Last night I was having trouble getting the reed right at the tip because the tip was unusually 'vague', but it turned out to be the patch had 'crept' toward the beak over time/playing and was now over the edge by about 2 hundredths of an inch. This happens to my patches and was not unexpected, but I usually find it when I'm washing the mouthpiece before a gig, and I just change the patch. But here I was on sound check with a creeping patch. I don't know about you, but I determined a long time ago that this is not a good thing and affects my playing - but I had no patches with me. So, I rolled the dice. I pulled the patch off and repositioned it, hoping it would make the whole gig, and it did. I got lucky this time.
I have two points here; if you need glasses to set up the damn mouthpiece, use them. If you use patches, make sure the patch is in the position you like and is firmly attached all around before taking the sax out to play.