I think a lot of what sounds cool in the long tail PI is the .1uF that's
on the opposite side. When you turn the amp up a bit you get more
of the tone of the PI coming through and that cap helps to add
some nice bottom end to the tone. Of course you can change that
value to whatever you like and I think the value depends on how
you structure the frequencies in the preamp (IE: coupling and
bypass cap values). Most pre-PI masters tend to roll off lows when
set at lower levels which might be some of the reason people have
to turn their amp up a little bit more (get some more bottom end
happenin') You can also play with the 10K that's in the tail of the
PI. 22K sounds nice and adds some more bottom end to the tone.
It's a thought! (ha, ha) 
 
Trace