If I'm not mistaken, you must edit this:
;Field of view (FOV) in percent. Integer.
That is if you're using 1.5.8 and above, then the above'd work. In fact, it's a command that's already in there, just tweak it as neccesary. 110 is the highest I know b4 things become fisheye. 90 is the lowest, methinks, but I honestly am not 100% certain if what problem you are discussing is really just the conflicts between newer ddfix and older darkwidescreen.
So maybe just uninstall the Darkwidescreen patch, and use the res. of your monitor in the ddfix 1.5.x series starting with 8, along with the FOVMod variable settings in ddfix too.
Because I believe the 1.5.x series can handle custom resolutions now.