Hi,
If I understand your question correctly, you want to know why a user download is assigned queue7 and not classified under other high priority queues. So if this is the case, here is my opinion.
COS configuration is left to user descretion. By MF or BA classifier, we are just assigning traffic into different queues. How those queues will be serviced depends on the scheduler configuration. There is no priority order set here for the queue, so it does not mean queue 7 will be services in the end versus queue 0 or 1.
As long as administrator is clear on how he wants to control the traffic, he can play with scheduler configuration and queue priority to define different service levels,
Hope this helps.
Thanks