Mikuni 28mm?????

gee... looks like i put a foot wrong here.... and also been misunderstood. i am exactly saying what you are saying, that there is no way to determine that one of us has more knowledge than the other. so considering that you do have a lot of experience, something seemed strange in your reply, read on..

so I am holding a VM26SS body in my hand as i write this (in the process of boring one ). Sure, it has a radiused STEP in diameter from inlet rubber clamp area to the main venturi area. But after this step, the bore has no TAPER, it is parallel. This is in difference to other VM types, or even CV types where the cross section at the slide is smaller than either cross section at the tract beginning or at the tract end (cyl head side).

In all my years of dealing with carbs, the first type are called parallel bore or constant bore whereas carbs that have a reduction in cross section at the slide point are called taper bore carbs. KZ650 VM24 for instance.

That was the root of our misunderstanding, never heard someone calling that step a "taper", but there is always a first

Last, and that's the funny thing, Keihin CR's dont even have that step (or taper or narrowing as you call it) and still work great. So the relative dip in barometric pressure is caused by the pure air speed in the tract compared to the still air in the float bowl.
real taper bore carbs just create even more of that pressure difference and hence supply better low end response