At present, there is no way to specify the type of flow hashing used in Stochastic Fair Queuing. The flow hash is constructed from source-IP + port and dest-IP + port, with round-robin dequeuing.
This gives per-flow (eg TCP session) fairness, so one host with 20 TCP connections can starve the other 10 hosts with 1 TCP connection each; this creates a significant DoS opportunity, which happens most frequenty when running a Routerboard eg as a hotspot or home gateway.
If the hash criteria is changed to only source-IP, fairness would be enforced across all hosts and will give a far better experience for hotspot users. It is already available in Linux’s SFQ implementation, so the RouterOS interface needs a new variable to control this.
Why not just use PCQ? Since we can’t have use the Random Early Detect. RED is important as it maintains lean buffering at the router to keep application latency low (ask me if you are interested for more detail).