Taipan .177 from hell strikes yet again!

I think this could be a clue... I don't think there is any place to screw a machine screw into a Huma reg on the downstream side. If you screwed a machine screw into the little brass nub, the regulator was installed backwards.
I put the screw in the large end not the small end. It's facing the same way as the Taipan reg.
 
Does the spacer control the size of the regulated air chamber? So a bigger one = more regulated air and higher potential fpe? Seems like there is limited ability to vary this due to the vent holes but for lower power and higher shot count spacer should be as small as possible, right?
As far as I can tell, the spacer serves to line up the vent hole in the air tank with the vent hole in the regulator. Depending on the configuration of the regulator, you might get a plus or minus in shot count.