Not sure that's correct, unless its a rather high crossover.
Not found graphs for the R3, but my graphs above and Amir's port measurement for the LS50 show port and woofer output being equal at 80Hz, unplugged. You'd want to plug it to get more from the woofer in the sub crossover region.
I was thinking of the Kef R3 but equally a 100 Hz 48 dB/octave crossover would still mean fairly limited port output even for whichever LS50 you're referring to I'd have thought.
I think this is a situation where you'd want the high-pass filter as high as you can get away with personally.