Nope, the foam is to stop teh fuel sloshing around when the level is low. The cup didnt hold enough fuel for the new pump so i've had to drill a couple of holes to allow more flow, the downside being the fuel drains quicker when being lairy. A 10cm layer of foam on the bottom of the tank should suffice.
Doesnt the n15 pump sit on the bottom of the tank? the n16 one sits inside a filter in the sender unit.