This is a great idea.

I think there is one catch, though. I think he's assuming that my accuracy is the same around the target that I am aiming for, regardless of where it is.

I find that this is not the case. As a "below average" player, I am still much better at hitting the triple 20, for example, then I am at the triple 19 - even though the triple 19 is theoretically "easier". What throws me is that the triple 19 is not centred across the board so lining up to it is more difficult.