I get what you're saying I think.
Visually, the contact point for a narrow angle kick,
is not that far from the middle of the cue ball and the line you want to aim.
Whereas for a wider angle kick, it's quite a difference.
But I think the single biggest challenge for kicking is accounting for the natural
shortening effect that rail compression causes. All banks start out going
a bit shorter than "angle in = angle out". They get "cupped" by the rubber
in the cushion and this sends them away from the rail at a sharper angle
than the normal mirror angle.
Then, if you have low speed or topspin, or if they're sliding but pick up
some topspin after travelling a ways, they might widen/lengthen out,
and end up back on the mirror angle.
But a lot of banks have none of the above and are always going to be shorter
than the mirror angle, so you have to compensate by hitting further up the rail
or using just the right amount of outside. Either of which require feel.
For very wide angles, especially at low speed,
the "cupping effect" is not so bad and the the cue ball
actually comes off the rail pretty close to the mirror angle.
And most people try that railfirst kick at very wide angles.
But they miss anyway. Why?
Because a lot of people misunderstand the basic imaginary mirror ball system
taught in books and online. They imagine a ball that is "mirrored" on the other
side of the cushion. Then they aim straight at this imaginary ball.
But if you do that, and the angle in = angle out, then you hit the object
ball right smack in the face. You aren't cutting it to the hole.
So you have to aim to CUT the imaginary ball, which is a little trickier.
http://i.imgur.com/du3NDYV.jpg
