First, some background: We set our sensitivity such that a certain amount of mouse movement will result in a certain amount of soldier movement. In it's simplest form, we have our hipfire at some cm/360.
If this were real life, when we use a magnified optic, that means that our movement is magnified accordingly. This is why shooters take such measures as controlling their breathing and heart rate. In game, where magnification amounts to a reduced FOV, this is very unwieldly. Having the same cm