Well... There may be more going on than you realize. It depends on your printer, but a lot of times when people are having trouble they can make the problem go away by specifying more points. Usually a 3 x 3 grid is sufficient. But sometimes, it is necessary to go up to a 4 x 4 or even a 5 x 5 grid.

Also... It would be helpful for you to do an M48 command at a few places on the bed and see how repeatable your probe is. If the number is too big, that directly factors into how well the Auto Bed Leveling can compensate. Can you post a few M48 commands for us?