The filter like the oil filter has to have liquid in it to function.
The fuel comes from the tank as a liquid.
The liquid is pressurized by the fuel pump and forced into the filter as a liquid, it then presses up against the float needle and when the float goes down, the needle allowed more liquid fuel into the carb.
If your trying to say that when the filter is on its side it will not fully fill ok I agree that can happen, like in my video. If the filter was vertical it would be 100% full.