How DOES one deal with such an overhand right counter to the jab (especially from a taller boxer punching down with that right)?

I have really long arms so this isn't usually a problem but I have seen it recently, and had to invent my own defense on the spot.

The guy who could do this is not much more experience than I am so he probably didn't know how to take advantage of my (new) openings when I did pretty much what you said:

I was ducking, fading left (outside his right), and/or roll blocking/parrying with my left forearm under his right elbow -- varying between 1-3 of these moves he stopped being able to hit me like that.

My knees are so screwed that ducking is a real issue for me, but he was tall enough that I didn't have to duck very far.

The whole thing also got me to concentrate on tightening up the return of my jab to guard, but that wasn't a big part of the problem.

BTW: I didn't seem to be messing up my stance since I wasn't (necessarily) stepping to do any of this -- although I also was continuing to move laterally to avoid standing in front of him.

What should I do?
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HerbM