I've not used a numbering system but manage some decent kick shots.
I'm not sure if the fiddling over the numbers is more than I could do because there are a fair
amount of systems that are different.
I put zero weight into numbering systems. Watch the OB as you stroke the CB. Feel the speed and don't worry about numbers. Numbering systems fail you because you have to adjust for table conditions. Might as well get a good look at the shot instead of worrying about numbers that don't work anyway. They might get you to within 10% of your goal, might at least "get a legal hit" but playing for a legal hit instead of something productive is a losing mentality. A legal hit only gives the table to your opponent, "sells the farm" in 1P parlay. Now if you have an actual plan, as in a safety or a make, then "getting a legal hit" is ok. But if your only goal is to get a legal hit your strategy needs work.
Understand that you can imagine angles and even a table matrix and the geometry holds true... if you have the correct speed and spin.
For a 1 rail kick, use top spin only. It makes the ball come off the rails consistently and it's all about speed control. Using side spin on a 1 rail kick is not smart. 1/50 times you might need to because of a blocker. But don't do it unless absolutely necessary. When using side spin you can't control how hard the OB is struck, which is important to give it a chance to make and not leave it in front of the pocket for an opponent.
Now boogie how can you say that you don't need side spin on 1 rail kick shots? Simple. You change the angle with speed. Harder shortens it, softer widens it, medium as the default is probably worth striving for. Where you hit the rail changes depending on speed, but it's best not to overthink that. Just set up an easy kick and shoot enough of them at different speeds until it makes sense. I do not focus on an aim point on the rail. Pretend the rail doesn't exist and let the shot happen. All tables are different, even depending on the weather/humidity/dirt etc. You'll drive yourself nuts trying to yoke all that into a system. We must adjust, and the subconscious is great at that. Sure, understand what playing long and short means but don't dwell on it. It takes you out of stroke/feel and holds you back.
For a 2 rail kick find the middle of the CB and OB and draw a line to the corner pocket. parallel shift that line to the CB and shoot. Again, just use top spin and speed control to contact. Look at the OB as you strike. I can't say why but the subconscious quickly figures out the parameters and you can be deadly accurate, pocketing balls or hitting them exactly how you want.
Now boogie, how can you say not to use side spin? Easy, practice it. I don't care how the numbers line up, if you can train yourself to do this without side spin you have much more options with speed control. Options on what you want to do with the CB, OB, separation, kick and stick etc. At some point you can start adding whatever spin to the CB but it's all about position, not the actual contact on a kick. It's a lot of variables. Best to stop trying to dominate physics with math and let the natural computer inside you do it.
For 3 rail kicks you might use a system, and you might want to use a touch of running english. It kind of still boils down to understanding how the CB wants to naturally go and getting as close to those parameters as you can. You might have to shift the first contact 6" from ideal and make up for that with speed and spin. On a 3 rail there is no shame in going for a "legal hit only" but if at all possible try to make something happen to your advantage. As you improve on 3 rail then only try to make stuff happen, get out of the "legal hit only" mindset asap. There are less opportunities for 3 rail shots in competition than 1 or 2 rail so it might be something to practice once in a while.
All that said, this game is 90% between the ears so do whatever you trust the most, but if you take one thing from this novella, playing for a "legal hit only" is not a winning strategy. Get the most out of your opportunities. Make it or lock them up in jail.