Riddle me this

1.9tdi ALH 

MBC fitted previously in between egr and the thing by the battery (n75?) could squeeze a wee bit of difference out of it.
 

MBC and boost gauge fitted on line presumably going to actuator (somebody had big hands couldn't fully check) and as you've already guest that's the vac line.

Bit of googling on someones part, "only" sensible place for a boost gauge is the intercooler pipe (black plastic by aux) drill screw in brake bleed valve etc

so the vnt has no boost lines? 

Then why on the holy heaven of earth did the previous setup some chap I know did; work? I was there. turn the mbc very very slightly and a subtle yet definite harder pull. Too far and limp mode. But surely it's the vac line... How chaps?