If you open the "autoexec" file with a text editor, you can use the "Search" function to search for words inside the text file. At least in windows you can use the search function.
Just type "width" and you can get two results...
"SCREENWIDTH"
"GameScreenWidth"
...one of them changes the ingame resolution, but for all cases I changed both.
Use "height" and you will find...
"GameScreenHeight"
"SCREENHEIGHT"
...I also changed both.
16:10 resolution that worked for me were:
1280×800
1680×1050
16:10 resolution that did not work for me was:
1440×900