Here is a method you can try. You might already know it, but here goes anyway.
I don't bank very good, so take this with a few grains of salt. It may work better for you.
It is basically a mirror system.
aim your shot at an imaginary pocket 4.5 feet directly across from the pocket you want the ball to go in, you will be aiming to a point that far away from the pool table. Hit it with whatever spin you desire, as hard or soft as you like, but make sure to pocket the ball in the imaginary pocket.
If it is a full table length bank, you are now aiming at a point 9 feet away from the pool table. This method works with all bank shots.., but only as good as a person can imagine that imaginary pocket, and hit it with the exact speed and spin, etc.
Best of luck
steven