Zandronum

I am playing with NVidia surround at a resolution of 6048x1080 and the aspect ratio is stuck at 4:3. I have attached one image showing Zandronum displaying the wrong aspect ratio: ...and one of GZDoom displaying the correct aspect ratio: You may ask, "Why not just play GZDoom then?" Because I want to play Complex Doom which is made for Zandronum.

Can anybody help me with this problem?

EDIT: I am not sure why the same image appears twice in a row, but the incorrect aspect ratio behavior from Zandronum is displayed in the image below.

I don't know the answer to your problem, but I do know that while it is possible to make something that works in Zandronum but not GZDoom, it is hard to accidentally do that, so Complex Doom will probably work just fine in GZDoom, but it will either be single-player or the awkward peer-to-peer multiplayer that GZDoom has.