I have the same set-up as toller (4" base and 2.5" fence). I was
afraid of too much pull from the base, so I joined the 2.5 and 4 with a
T connection the 2.5 is a the straight shot to the dust collector, the
4" is joined at 90 degrees. Seemed like a good idea, don't really know
if it works or not, seems to.

2.5 fence-------------------dust collector
|
|
4" to base

Dave