Some good points.
A possible workflow here could be to adjust once, and stay till changing tool.
Advantage, quick and easy, no UI easy to understand.
Disadvantage, hard to reproduce after one changed tool and come back to tube.
Controlling tube size distance to camera feels a bit undefined. A slider to control radius would give very quick and intuitive control from my point of view.
Second finger hold and move pencil vertical for taper instead of mirror.
Mirror gesture feels a bit strange to me.
Second finger hold and move pencil horizontal for division X. 