Check that first, don't think it will, normally though I would of thought it would be the opposite, I.E less boost as the spring is weaker therefore not keeping the gate shut, but clearly it can happen as above. Don't think it will be a boost leak as you are reaching that figure therefore so clearly it's reaching the plenum, the missing is probably actually overboost protection.

If not the above maybe something funky going on with the Amal.

Martin