TCP delayed acks not being delayed?

[RW]

I have a 1MB/0.25Mb ADSL connection and have an IPFW rule to prioritize 
outgoing empty acks. If I download a single file with kget at 100 kbytes/s, I 
see that the rule gets hit at a rate of  50/s: ie a little under 1 empty-ack 
per incoming packet.

I have: 

net.inet.tcp.delacktime: 100
net.inet.tcp.delayed_ack: 1

which I thought should limit each TCP connection to <=10 empty acks per second