Arramis

Have a look at this thread:
That's the latest forum where we actually took a good look at how sensitivity is really perceived. And then I guess we've just been discussing in a whole bunch of other random forums. It really is a mess. Not very helpful to new users. I don't know what DPIWizard will do about it but he did say he was going to make a new version of the calculator. He'll probably make some new videos and explanations as well.
Still not sure what everyone else's position on the best method is, but personally I believe it's 0% monitor match and I am certain I won't change my mind anymore. Unless Capta Praelium is still working on his method, but I think it won't work because I tried something similar and disregarded it as it didn't follow the gear ratio principle. @Skwuruhl has been saying it's 0% for a long time.
Monitor matching is essentially the gear ratio so you could still mathematically be okay to use higher percentage monitor matches, but they are just not as good as 0%. And there is definitely not a perfect percentage as they are all arbitrary and affected by distortion. Same goes for Viewspeed. Viewspeed was another great idea but there wasn't really any proper logical reasoning behind why it would sync sensitivity. But if it works for you, keep on using it. Muscle memory you have developed over the years can play a big part in what you feel is wrong or right.

When FOV's are similar any conversion method will give the exact result. When the discrepancy between FOV's is noticeably high you should probably stop converting via 360 method.
I personally use a low sensitivity, therefore 100% mm brings more versatility and room to improve IMO even though 00% is the way to go.
You do you, what works for me might not work for everyone.

To be precise, you can use 360 Distance only when FOV is exactly the same. But even then, there's no point in doing so because if you monitor match you will also get the same result when the FOV is the same. Easiest way to do it is to just choose your monitor match percentage and convert everything with it. Why bother discriminating whether FOV are close enough to use 360 Distance when it's unnecessary...
You can honestly use whatever monitor match percentage you want because they all follow the gear ratio principle but 0% is the most correct and best at tracking/precision at the crosshair. It's advantages far outweigh those of higher percentages.
Also, keep in mind that it's ill-informed to think in terms of percentage of the screen, because we know now that perceived sensitivity changes according to size and distance of your setup. Your percentage will not translate the same to another person's setup. It is all arbitrary.