Ok, a little more info.
With a dual port external gate, you can set the WG up such that it stays pinned-the-fuck-shut till the MBC comes online.
With a single port EWG the WG sees manifold pressure all the time. If it has an 8 PSI spring, then it takes a net of 8 PSI acting on the diaphragm to overcome the spring and open the gate. You get 8 PSI boost.
With a dual port, you have a port on each side of the diaphragm. So say you want to run 14 PSI and you have an 8 PSI external gate. Then you hook the the WG up such that when you're making boost, the top WG port sees boost, and keeps the fucker pinned shut. The more boost you make, the more of an air spring builds up on the top of the diaphragm to assist the spring in keeping the WG shut.
The other port is referenced to a MBC though. So when you're making 2, 5, 9, 11, 12, etc PSI, that port never sees boost as the MBC hasn't opened yet. So the WG stays pinned shut and you get the best spool possible.
Then when you finally get close to target boost, your MBC opens. Then, all of a sudden X PSI (whatever the MBC is set to) shows up on the other side of the diaphragm and cancels out some of the air spring that's there from the top port. Then the WG opens to regulate boost.