My classic shell start button isnt properly centered when compared to the one on my other taskbar.. (its a custom button set at 1.42 size)
and its to far up and to the right compared to the one on my other desktop.
maybe you could add some advanced settings "start button Offset X" and Start button Offset Y"

and the top 5% of the icon is cut off (when in hover over mode), but not on my primary display without display fusion but i read your trying to fix that one