What happens with JB in my personal opinion is the following:
Given a generic lateral force vs slip angle
There's a maximum. Let's say the maximum is at 100 grip units. That would be the ideally fastest lap. But there are two ways of getting 90 grip unis. One is below best slip angle and the other is above best slip angle. I believe Button manages to stay below the maximum.
At higher slip angles portions of the tire patch are sliding, and you get less increase in lateral force with an increase of slip angle. This is called the transition region. As the curve tops out, more of the contact patch is sliding and the tire produces less lateral force. After the peak of the curve, lateral force can fall off 30% within a few degrees of extra slip angle. At these high slip angles most of the contact patch is sliding, producing a lot of heat and wear.
Bye!