I think we're almost on the same page. If you increase pressure, you increase the amount of fuel that the computer expects to deliver with a certain length pulse. The computer will see this as a rich condition and reduce the length of the pulse until it gets the air/fuel ratio it is programmed to keep. You still have the extra fuel you need at maximum load but the computer has adapted to the extra fuel that it doesn't need at lower load conditions.
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351W 89 Mustang GT Convertible