The contact area never changes size. This is based on the size of the balls only.
What is being discussed is the margin of error which is that area on the OB that the CB can contact and the OB goes in the pocket.
The contact area for a center pocket shot is always the same no matter distance.
There is a difference in just putting the ball in the pocket and putting the ball into a specific part of the pocket. Just putting a ball in the pocket is what margin of area does. To put the ball into a specfic part of the pocket requires contacting a specfic area on the OB and not a range of area size that just allows the ball to go any where in the pocket.
I'll agree to a point... You can always pick a specific part of a pocket when you need to cheat the pocket for position... But what if the pockets play tight and you're not very close?
If the pockets are tight you may need to play shape differently than on a table with loose pockets. That is why the OB contact area matters on different table pockets.
I prefer to play tight pockets, but then you don't have the same positioning options as a table with sloppy pockets... where you can hit any part of any pocket from anywhere.