Boost pressure

[Sweety]

On a 2.7TDI T2 am I right in thinking the standard boost pressure should be around 0.9bar / 12-13psi ? The reason I'm asking is my old gauge used to show 1.2bar but the new gauge is showing 0.75bar now I'm sure the old gauge was over reading a bit & at time would get to 1bar then jump to 1.2. What I noticed when fitting the new gauge was the T that came with it had a brass insert with a tiny hole in it on the part that the hose fits on to go to the gauge but the old T didn't have this so was wondering if the full boost pressure isn't reaching the gauge: if it makes any difference the new gauge uses 3mm ID hose where the old one had 3mm ID 3.5" long which went into a brass fitting & had 1mm semi ridged pipe coming out of it to the gauge only thing I can think of is poss swapping over the It's to see if that makes any difference