Using Focal Length Feature doesn't account for change in aspect ratio?

[Magico.-]

Hi there,

I was just wondering if anyone knows of a way, or is aware that using the focal length feature from one game to another while using a stretched aspect ratio e.g. 21:9 in Rainbow Six Siege to say Valorant. It doesn't account for the change in aspect ratio when giving you the resolution to customise towards, it is the same output when using the same FOV but different aspect ratio. I wondered if anyone knew of a way to figure out what the resolution should be if you are using a stretched resolution?

Thanks