Sorry, I was answering in my previous post regarding the present JB systems.
The quote you highlighted for your question relates to the new Pay Related JB scheme which starts from 1st April 2025.
I would presume that this will also operate in a similar manner as the existing systems i.e. class A or class S earnings will apply. But not both together. This is just my guess.
The existing systems will continue to operate alongside the new Pay Related JB system, so if the existing systems are more beneficial to you they would be applied.