If you set it to Legacy (i.e. lock it) all scopes will be matched to 0% monitor distance. This is the slowest match, ideal for tracking objects etc.
For Relative, 75% (or 1.33 in the config file) is the default method for a lot of older games like CSGO, while 100% (1.7778 in the config file) is more commonly used for new games.
Common for them all is that they match sensitivity to a specific point on your monitor. So regardless of if you are aiming ADS or with a 7X scope, moving to this point will be the exact same movement.