Proper working QoS is only possible on the outgoing interface of a router or host, where the bottleneck begins. Everything else is a hickup and not subject to work as expected or has a successful result.

-------------->-------
           Queue 1    \
           --->---     ---->--------->--------->---------------
Big pipe   Queue 2      Queue 1 / Queue 2 / Queue 3   Thin Pipe
           --->----    ---->--------->--------->---------------
           Queue 3    /
-------------->-------