If you want some hard numbers from my attempt at an explanation earlier, here you go:
Imaging being 90yds to pin. Now to compensate for the wind, or a pull swing, you aim 10ft from the flag (the important thing to remember is your actual triangle mark is 10ft from pin on the green) will you need a shot distance of 90.1 yd, with the angle produced for the adjacent side (ball to pin) and the hypotenuse side (ball to aim marker) is 2.12 degrees. (this is using a right triangle model and the old useful tip "Old Harry And His Old Aunt" to calcuate theta).
Now you use the aim mark if you think the line is right but the marker instead of 90yds is at 20 yds (because of higher ground the aim mark lands on the higher ground, not the green, it still looks like you are aiming 10ft right of pin). That gives us the same 90yds to pin, but 20 yards to mark. Since the angle is unknown, I am going to take the line to pin and stop at a spot on that line 20yds in front of ball, now go 10ft right and create a right angle triangle to calculate the angle (assumption I know but it should get us close). We get a 20.18yd hypotenuse line (ball to aim mark), and an angle of 9.46degrees.
Thats over 4 times greater in angle created. Lets say you used that faulty marker on 20yds away to hit your shot, and your attempt is to hit a 90yd shot, using that 9.46deg angle created your shot will land approx 45ft from pin or 15 yards. Do the same thing from the fairway from 200yds out using the same angle you are going to ended up 33.33yds right of where you think you are aiming.
So you can see, dont trust your aim spot unless that marker is aimed on the green itself. What you thought was aimed 10ft from flag was actually 45ft from flag
I know my numbers are off by a few decimals, but I didnt feel like calculating the numbers on an acute triangle in the second part, cos theta is easier to do on a right angle, then calculating all sides and angles on an acute angle.