Ok, my thoughts on this are based on some experience with many different bats and looking and the impact marks made by dirty balls on a scuff sheet!
Firstly I think that the pitch you play on and the bowlers you face are irrelevant. This slightly controversial statement is based on the view that you face fast and slow bowlers, tall and short all of whom make the ball bounce in different ways, so you need to be prepared for all types of bounce and speed.
As a result the batsman will play shots in his favoured areas and should adapt them to the pitch and the bowlers.
This leads me to my next point the batsman and the weight of the bat.
A batsman will have certain favoured shots, these should determine the middle position on the bat. When the ball is bouncing more you need to play the shot when the ball is more pitched up to you than when it isn't bouncing so much. The cross bat shots become a matter of timing.
The weight could vary, lighter bat for longer forms, heavier for clearing the ropes, but the middle should be in your favoured hitting point on the bat.
My suggestion is therefore that I agree with the corollary of Richard. However, I also believe you can, with practice change the way you play, the shots you like to hit and thus the middle position you want for your bat. But this would take too long for most people.
The reality is there is a reason why mid-low middle bats are the most popular because that is where most people are used to having the middle of their bat and their game adapts accordingly.
So all that waffle is short says.. you need to know where you hit most balls on your bat and it helps if the middle is in the same place.