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Here is how the actuators work……..
The actuator spring and preload are what keep the wastegate flapper door closed.
The reason the actual minimum boost is lower than the actuator preload setting, is because the wastegate flapper has exhaust backpressure pushing on the flapper door, on top of the actuator receiving the pressure signal.
The tighter you make the preload of the actuator, the higher the minimum boost and the *more* likely the boost will spike.
Making the preload tighter causes the spring to compress more and limits the travel of the actuator for how far it can open.
Having a tighter preload will allow boost to spool sooner. This is because the wastegate door stays closed longer allowing more boost to build before it starts to crack open and regulate pressure.
A lower actuator preload will lower the minimum boost, spool the turbo slower, is more likely to have the boost taper off at higher RPM.
The boost signal to the actuator is required to regulate the boost, if you do not have a boost signal feeding the wastegate, you will have maximum boost.
A boost controller allows higher boost by regulating how much boost signal is allowed to get to the wastegates. By delaying the signal and sending less pressure to the actuator, the wastegate flapper door stays closed longer allowing more exhaust to feed the turbine and produce more boost.
Running both signals together to a boost controller is correct, but thinking that offers safety if one boost signal comes off on one side is not correct. If you loose a boost signal to the actuators anywhere in the system, (before or after the boost controller) even one side of the tee to the actuators, this will cause both actuators to not receive pressure and the turbos will make maximum boost.
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