I finally fixed my problem after a complete reinstall of FSX and checking the fog from above after each add-on installation.After installing one of the clouds-replacement addon the fog disappears and can only be restored by replacing the original cirrus_overcast03.bmp in the fsxtexture folder.Note that DWC contributes to that by always ignoring the fog layer no matter what option is selected in ASE gui.From my experience the only way to see a close to reality cloud and fog effect is to use either standard or SCT depiction modes.Example below

My experience with DWC and fog is not like you describe :)