How does the upper bore affect the overall tone? What are the possible negative and positive affects of reaming and upper bore?
According to my experiments (with selfmade shticks only of course and no guarantee for “absolute truth” 
; other experiance more than welcome) widening the upper bore makes back-D, C, B and A area sound brighter (more “free”) and the second octave easier to get but at the same time might weaken the harsh-bottomn-D.
Cheers.
Hans