Well FP can rise when the air dome diaphragm hardens and no longer acts as a damper. Now on compression of diaphragm via spring pressure you windup with a higher pressure since no deflection of the air dome. Whether it is so high to overcome needle pressure not sure but plausible.

EB do require a lower pressure then the orig carters. They use a smaller float and larger orifice which means less force available on the needle to hold back the greater force generated by the FP pressure when a larger orifice is used. Think Brake cylinder diameter. Same effect.

What seems confusing to me, is the bowls probably start out dry or at least low. Your only cranking at a slow rpm and at some point the car should start before the bowl is so high it overflows. So maybe some other issue preventing proper starting that is ultimately leading to a flooded engine too.