My technical education (mechanical engineering) made me look into the zoom sens a bit deeper then most people. I've attached a chart which puts the sens scale factor against the zoomfov. There are 3 lines drawn:

1: Automatic sens scaling by Q3 (using +zoom)
2: Sens scaling by cg_zoomfov / cg_fov
3: Sens scaling by tan(cg_zoomfov/2) / tan(cg_fov/2)

The 3rd one I made up myself. Because your 3D view is projected on a 2D plane (monitor) the size of an object on the screen depends on the tan(fov/2). Draw a rectangular triangle from the viewpoint to the projection plane to understand this.

Notice how line 1 is some sort of combination of lines 2 and 3! Any mathematical genius out there who can clarify this?