The moral of the story then being that if you want your outbound ack packets to match a firewall ackqueue, then you need to make a floating rule that will match packets coming in on the WAN. For example, for an http download, make a floating rule that will match packets from source TCP/80 and ackqueue/queue to ackhttp/http or something like that.
Now, if I could just figure out how to set up my queues…