W/G vacuum question
 

got my 91 integra boosted, been running great, but did not have a vaccum line on compressor for the W/G. i installed a nipple on the intercooler pipe just 3 inches from turbo. i have a 5.83 spring and was running 4-5 psi before when my W/G source was vaccum at FPR. now it is 8-9 psi, but it is consistant. this is where i want to be, just wondering why the difference if no change in spring. set up is stock B18B, t3 .48/.42, 38mm external W/G w/5.83 spring, tubular manifold