-Wastegate Duty Cycle (WGDC) directly controls the amount of boost we produce on our wastegated turbo's. It is controlled via vacuum lines, which electronically controlled through the DME. What the bolt on's do (DCI and DP specifically) is reduce the amount of WGDC needed to produce the same amount of boost. This is because the turbo's are working less to achieve target boost, and won't need as high of a value of WGDC.
-You don't increase boost through bolt on's, it's increased through a tune. The factory DME will actually increase boost on it's own at higher altitudes, in order to reach the factory load target.
-If you have a major boost leak, the DME will throw an underboost code because it can't reach it's target. You have the right idea regarding boost leaks: Loose clamps/broken piping/pinholes/bad FMIC welds/and more can all cause a leak in boost, because pressurized air is escaping (Like a small hole in a balloon)
-The DME itself measures the boost pressure. You can install a boost gauge, install a supporting tune with logging capabilities/gauge hijacking, etc to monitor boost.
Hope this helps. Put the
suit on, you will need it