There’s no provision for adjustment that I know of for when the Vboost comes on. I’ve had a couple of the controllers open and I’ve never seen a potentiometer in there. There are products on the market - or you could cobble something up that routes signals from two coils into the controller and fools it into thinking the engine spinning faster than it is. Other than that…
V Boost cable adjustment an butterfly synchronisation are described on pages
5-13 to 15 of the Service Manual.
There are devices such as T Boost that will open the butterflies earlier but IMO any benefit is in the head rather than on the road.
Or, get an Ignatec ignition module and dial in the settings of your choice. You'll have the ability to change opening of the v-boost without taking anything apart, using the supplied USB cable. And you'll have several other useful features the factory didn't include, like a rev limiter.