I have a 150mm hub to hand (newbie bought the wrong wheel set) and the extra width has been added (compared to the regular 135 hub) between the hub flange and and brake disc.
With the boost hub on my girlfriend’s bike, the spacing between the disc and flange is the same as the 135 hub and the extra width has been added between the flanges.
I would give you proper measurements, but 2 of the hubs are being used in wheels and I can’t get a ruler in there.