Pressurizing the space under the pump diaphragm causes fuel pressure to increase at a 1-1 ratio with boost pressure. This is how you get a 3 psi pump to push fuel into a carb pressurized to 6 psi for example.
As to placement. There is no impediment to airflow between the fuel pump base to the aluminum casting below the diaphragm. If there was we would not have to seal the pump shaft with an o-ring
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