Linux Traffic Control

In the GRED queueing discipline of linux traffic control, we can define
around 16 Virtual Queues with different RED parameters for each one of
these. As far as I think, while applying RED on each of the virtual
queues, with the grio option set, quave(the average queue length) of a
virtual queue with priority= n is given by the sum of the virtual
queues with priority greater than n ... I have the following questions
:
1. Is my understanding correct ?
2. What if I set the priority of two virtual queues as equal ?
3. If I want that the Average queue length being used before dropping a
packet should be equal to the sum of the average queue length of all
the virtual queues, where would i have to make changes in the source
code ... ie, just making changes in sch_gred.c would suffice or I have
to make changes to some other files also ...

Rahul