ipnat transparent www proxy question

[Markus Kovero]

I would like to do transparent www proxy for nat-network which is
172.16.0.0/24 and wwwproxy being $ispcache
I told ipnat to do:
rdr xl0 from 172.16.0.0/24 to any port = 80 -> $ispcache port 8080 tcp

but all www connections go straight through, not through cache.
xl0 is LAN interface.

Any clue?

Markus Kovero