Assume as above.

The maximum difference is the maximum PA or the minimum PB. Only in these two cases can the biggest difference be obtained.

When PA is maximum. That is, the diameter P(0,-1). The difference is 2- the root number 2 is about = 0.6.

When PB was the smallest. That is, when the coincidence degree of p and b is 0. The difference is AB length = root number 2. Significantly greater than the former

So when the maximum values of p and b coincide.