That's why you use 76.19% on that 21:9 panel, and 100% on that 16:9 panel, to maintain the same match lol. Of course the percentages aren't going to line up when the calculator is using a percentage of the horizontal, which is dependent on the aspect ratio. If you think of it as a multiplier of the 1:1 aspect ratio, then both examples in your picture would have the same value and the same match point, which will be independent. In that example, it will be a 16/9 coefficient, 1.778. Any monitor match % results in the 'gear ratio', it just depends on what your measuring. Anything above 0%, it is a simple ratio between the angles, they all follow the 'gear ratio' principle. Compare 90/45 Hdeg 4:3 when matched to 4:3 and you will get 2 * the circumference, same thing when comparing 16:9 values when matched to 16:9, or comparing Hdeg or Vdeg if you are match to 1:1 (depends if landscape or portrait). For 0%, it's not just naiively dividing angles, it's the tan ratio, so compare 90 and whatever fov is exactly half of 90, (it is 53.13) and you will get the gear ratio. All monitor match percentages follow this principle. It just depends on where you measure.