[72SB]

The position of front line is not the problem.

Your PV is sensing a change which triggers the switch. Whatever direction it moves, that part (front or back) has a leak you need to find

...or the PV is bad which is rare but given source of replacement parts used in these kits, way more possible now.

Power brake disc typically use a 1 1/8" bore MC but that would not affect what PV is doing. larger bore just means less pedal stroke as the booster assist does not need the stroke a manual setup needs.