In the meantime and to get closer to you target, you could try to reduce the interaction priority for workgroup B from 50 to a lower value (like 5, for example).
As interaction priority has a direct impact on interactions scores calculated by the CIC ACD engine and these scores determine which queue interaction will be delivered to an agent first, reducing this value will make interactions in queue A score comparatively higher than those in queue B, even for high waiting times.