I have read that posted before and found the result odd too when based on that information.
If you think about it though, boost is the amount of air forced through the system and into the intake. Freeing up the restrictions in the system should thus allow more air to be forced through and boost should increase not decrease.
The only way that pressure should be lost is if a major dead point is created in the system or if a substanial amount of velocity is lost. The only way that logically this could happen is if diameter of the system somehow was significantly larger than what the SC require. Similiar to putting 4" exhaust on a 4 cylinder engine. The result would be a drastic loss of velocity and flow.
We know that this is not the case in the factory design as the lower IC tube is horrific in shape and ID.
Other than this modification and a 10 % SC pulley the previous owner put on, my car is bone stock. After installing my modified top, intercooler and IC tubes I warmed the car up and went to test performance. From a standing stop, the car smoked both tires for 30 feet. Couldn't do it when I first bought it. I can post a picture of what is left of my Yoka's.