Cockpit FOV maximum zoom?

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I have set F1 cockpit FOV for all 4 planes that I own to be 60 just like in the F2 plane view. But when I start a mission, the F1 cockpit FOVs are 72.9 or 73 instead of 60. Is FOV 72.9 the most possible zoom in from cockpit? Or is it some glitch or bug?

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Actually, there is always a difference of around 13 degrees. For example, if I want a FOV of 60, I need to set the FOV to 48.5. After I quit the mission, and then start it again, I will have FOV 60, but if I reset the cockpit view to normal, I will have 48.5 FOV. Accordingly, the Mustang for example starts with FOV 94.1, but when I reset the cockpit view to normal, then I get FOV 80. The Mirage starts with FOV 78.4, but when I reset the cockpit view to normal, it becomes 65.