I'm trying to figure out what the booster is made of exactly. If the plug on the back of the alternator is used for voltage reference and you use a diode to drop it down .7v (assuming a silcone diode is used) then the voltage regulator should boost the output voltage to make up for the loss that it sees.
I'm not sure where 1, 1.5 and 2 amp diodes come into play here. Amperage is simply the amount of juice that the diode can handle. It has no effect on the voltage.
What would make sense to me is if the stage one had one diode, and the stage two had two diodes in series (unless they used a zener diode).
