I don't have the answer to this, but have to think that this is an incredibly complex math equation.
The challenge is: speed.
The ball is not traveling the same speed across the entire grid and as people have said before, the break affects the ball more when it is moving slower. Inside 5 ft you may be able to use some what of a linear equation, but the further out you get the more complicated it is going to get, IMO.
Now that you can change the dots to move forwards and back, you might be able to come up with something, but what you come up with may not be anywhere near the equation that WGT uses.
Its an interesting question and curious to see what people more adept at math than I am have to say