It took me a while to figure it out too but here's the Reader's Digest as I understand it.
Minor or Major power factor is related to the energy of the bullet. It's the weight in grains x velocity in FPS / 1000. Minor scores the same for a center hit but less points for the outer regions than Major. The idea is to encourage the use of "preferred" self defense ammo calibers and prevent the use of "powderpuff" loads as used in other shooting sports such as the reduced power cowboy action stuff.
Production- stock pistols, no mag wells, no fancy grips unless factory options, no sight changes, double action first shot out of the holster and single or double action OK from that point on. All scoring is done as per "Major" loads. There's no power factor scoring correction in Production. And there's a 5 lb minimum double action trigger pull before release. Single action can be as light as you can stand but don't go crazy or you risk an accidental discharge and the end of your day.
Standard - is anything but...

Mag wells permitted as well as single action only so this is where 1911's show up. Minor and Major are scored differnt points so the move is to use something like .40S&W or other loads that meet the Major power factor. Mods can be done more freely but you still need iron sights. No compensators allowed.
Open- Full on race guns with red dot sights, compensators, mag wells, open mods to triggers and any other aspect of the gun. Minor and Major are used for scoring but in Standard and Open I'd say everyone shoots a round and load that meets Major.