If you are using the PID controller in manual mode, it shouldn't matter where the temperature probe is located. When boiling, the controller should be in manual mode and you should be requesting the output to 100% till the boil is rolling, then throttle back.
In manual mode, the controller does not use PV to control the output. Basically ignores the temperature probe until its switched back to auto mode.
This^^^^ The probe has no impact on the boil if you're in manual mode, which I thought you were because you had set bAST to zero. You could completely disconnect it and it shouldn't have any impact.