As it is right now if you change the mouse sensitivity but want the marksmanship sensitivity to stay the same you have to either use inverse proportions or just do some testing ingame. The ideal solution to this problem would be to make these sensitivities independent from each other, but it would probably be quite hard to implement without screwing the relation they have right now.
So i thought that the problem could be easily solved by adding a checkbox in the mouse options menu to enable or disable the automatic adjustment of the marksmanship sensitivity. What this does is, basically, perform an inverse proportion to keep the same marksmanship sensitivity in relation the the normal sensitivity.
For example:
Mouse sensitivity 10.6
Marksmanship Sensitivity 0.282
If i want the same marksmanship sensitivity with a normal sensitivity of 10 i'd want the first one to be (10.6*0.282)/10=0.298
Here's the menu as i thought it.