From user manual there is not a clear explanation of QOS configuration behaviour

My question is:

If I setup upload and download bandwith from my ISP contracted service, then I select High Priority devices, medium Priority devices and Low Priority devices, how bandwith will be shared among device in specific cases?

For example

Case 1- Bandwith is lower than demanded traffic,
How bandwith will be alocated between devices, as priorities percentages have been configured? , so for example if high priority is 60%, medium is 30% and low is 10%. Alocation is fixed or dinamic? What percentages mean? Can be that hight  priority devices will be guaranteed with 60% of the bandwidh? What happens when High priority devices are much more than low priority devices and low priority devices are not demanding traffic? In this latter case the high priority devices will compete among them for the 60 % or they will "steal" bandwith from the medium and low priority percentages?

Case2- Bandwith is higher than demanded traffic
How bandwith is alocated between devices? As fixed configured percentages between high, medium and low priority, are devices traffic to  be alocated within the configured percentage limit , regardless of demand from the other configured users? For example, at a certain moment, no high priority device is demanding traffic and at the same time time a low bandwidh configured  device is demanding for traffic. In this case, there are 2 possibilities, that router, regardless that there is not traffic being demanded by high priority device, will not allow the low priority to ocupy the full available bandwith,  or the other possibility is that QUOS behaves completely dinamic and the low priority will be allowed, in this case, to accupy the full available Bandwith

Hope the question is understood and somebody answer me how behaves the QOS configuration parameters as the user manual is not very detailed in this matter.

Regards