Modeling involves either tracing, sourcing, or measuring for driver files of spl and impedance, and placing them in various programs to model your xover. Calculators are not indicative of real world results like a simulation can be.
If you place the resistor before the xover circuit in series, then it will minimally affect the circuit as it stands, as well as the xover point. Positioned after- that can tilt your response down, as well as shift the Q of the xover filter (Fc of xover filter remains the same, but the Q shifts) and maybe shift the F3 or F6 of the rolloff to a higher frequency. It depends on the room, boundary locations, drivers used, as well as implementation. Lots more variables than just impedance to look at.