Please explain why mismatched Q's better in Pushme Pullyou

[RLBJR65]

I built Tim Escobedo's Pushme Pullyou.
http://www.geocities.com/tpe123/folkurban/fuzz/snippets.html

Tim stated that matched transistors need not apply. Very true! What I found was that the more mismatched I could make Q2 and Q3, the more pronounced the octave was  

I'm still learning a lot and really just stumbled onto this by playing around. I was trying to see which transistors caused what kind of affect to the circuit and the sound.

Can someone please explain why mismatching Q's makes it sound better?

This is what I ended up using in mine.
Q1 2N5088 hfe 465 - Q2 2N2222 hfe 170 - Q3 2N5087 hfe 450

I removed the 470ohm from the ps and subbed 470K's for the 500K's, on Q2-Q3 base to collectors.With these mods. It is a clean octave up to about 1/2 gain, 1/2 to 3/4 sounds like it's slightly over driven but still fairly clean and after about 3/4 gain I get an octave fuzz that can get some good feed back going, its nice not really over the top.