It depends, some do prefer a change when changing monitor size, others don't. If you want to get really technical you should also consider the distance from your eyes to the monitor as well, as the the angular size of the monitor changes.
I know... It's amazing that a game series that literally focuses on sniping just have a slider with no values. It's actually possible to count pixels (or rather every single notch on the slider) to set the sensitivity more precisely. I can add calculation for that too if it's of any interest, but it's kinda hard to set it this way without scripts/macros that move the mouse exactly one count.
Ideally you should use MDV 133% for everything and not Viewspeed Vertical in this case. Viewspeed Vertical and MDV 133% is almost the same though, but MDV 133% will match USA 133% perfectly.