Horizontal mouse look speed

[lepros]

Is there any reliable way to adjust horizontal look speed? I am having to move my mouse about 20cm for a full 360 look and im ending up bashing stuff on my desk.

This problem has cropped up since I started using a 3840x1200 widescreen monitor. It makes no difference whether i play in windowed or fullscreen.

I have searched these forums and have tried all the fixes:

Adjust max fps, this doesn't really help much, if i set it all the way down to 10fps along with mouse sensitivity up to 100 the horizontal is better but not perfect (15cm for a full 360). Of course as the mouse sensitivity is all the way up I am having to be very careful with my up/down movement as it is way oversensitive in that plane.

I have changed the mousepointerspeedmod in the .ini file to various values, had no effect.

Ive tried using borderless but that didnt help.

Is there any fix for this?