The blanks & the area by the reel seat to the butt end, are they all the same rod blank?  I mean they are not 2 separate pieces put together by the reel seat?

I guess my eyes are getting old, my Shimano Cumara & Carrot Stix look like from the reel seat to the back that the graphite is of a different diameter.

Am I wrong or right about this?

Would it be that the fact that the rod blank's diameter get bigger as it moves away from the tip thats why the blank is different size at different point?

Hard to say how the Shimano rods or the E21's are built, (unless it is a collapsible blank, i e flipping sticks down into the handle, or an extension has been added) most all split grips are built on a one piece blank.

Could be what your eyes are seeing is the blanks taper.....

Tight Lines!!!!