it should not matter. It that is an internal one that fits in the tank, it won't affect the pump. There is no "head" if both ends are in the water. Same goes for external filters. If both ends are in the water, there is no "head" to consider. Head would come into play if you had a wet dry filter for example. There would then be a pump to get the water from the reseviour back up to the tank. Since a wet/dry filter is an open system, the gravity pulling water down from the tank does not help push water back up to the tank, hence the "head". (since the pump has to fight gravity)
