The visor mod on the FR 3.5 for example is dependent on the FOV. I use a FOV of 27 and I only see a small selection of the visor, not even the banner on the top. When I opened the visor_cam.dds, I saw there are different layers with smaller visors in there. Just what I would need for a low FOV value. Is there any way to switch between them or what are those different layers for? Any other solution to see the whole visor with lower FOV values?
A single DDS has multiple resolutions for different on-screen sizes (if a texture is going to be drawn on screen, flat, 20 pixels wide, there's no point using the full-size 1024x1024 texture to do it. So a much smaller one is used instead). It's nothing to do with a different 'working size', unfortunately. The size of the visor seems something that could be adjusted to suit the FOV though. More a wish list item than anything else.
When you create a dds file, the multiple images are typically for LoD (level of detail) which the game engine uses to render objects at different distances from the point of view. The further the distance, the smaller the image used to save memory. For the visor, I would think that the game engine never uses anything other than the largest image, however it appears that when wearing the helmet, the game engine treats the visor view as the windshield which is unrealistic. The helmet view with the visor should be treated as a static image over the camera lens at a fixed distance rather than something that scales.
