You could try and drill a 8 to 10mm hole in the blocking plate to eliminate or at least reduce the errors. Seems the GU8's tend to boost a lot higher from what I've been reading but I'm going to install a dawes valve on mine just to be sure and limit the boost around 16psi. I'm getting cruising boost of 22psi when cruising with no load at around 100ks...There was a good thread on here somwhere how the boost spike works when cruising