1. Legacy will lock the scaling to a base FOV of 65 Hdeg 4:3, and scopes will stay the same regardless of your actual FOV settings. Legacy was previously broken in the game where the coefficient was applied when legacy was on, but it's fixed now so I will add support for this again.
2. Gradual is the most intuitive yes, the others can result in a sudden sensitivity increase or decrease.
3. Both methods will work with the selected matching method, which one is most preferred I'm not sure.