My reference to the article was only to suggest that running a 4" hose / duct from an extractor through a cyclone, and "then" moving into 6", would reduce airspeed.
In theory (and in practice) it would be better to maintain the 6" diameter through the cyclone and into the extractor itself...
I think your problem of chips being left in pipe / duct is due to the fact that you have an extractor / cyclone that has a 4" port, but that it's connected to 6" ducting.
As soon as the 4" moves into the 6", it's going to lose a massive amount of airflow.. you may be better using 4" ducting...
I have a Startrite 401s I am selling, but I'm in South Wales unfortunately.
In fact, I'm brand new here and only joined as I was searching for an idea as to what to ask for it and found a link to someone selling one on this site, but that was from an old thread.
Sorry, not exactly any good for...