As a long time avionic's tech, I think some body's radio or test set is off freq. Here in the states the 25 KHz radios are to meet 30 ppm or better. If my math is correct (big if) 119.875 * 30 = 3596 Hz, or 3.596 KHz which make more sense.
I agree that if the aircraft receiver is off freq, the farther away you are from the station, the worst the received signal will be.
Here in the states, with remote sites, all of the transmitters are on the correct center frequency. Center can key the one closest to the airborne aircraft. Not sure about the other side of the big pond.
Oh, and I think BFO is typically only used for CW communications, not SSB. Or at least that was the way it was when I was doing position reports on HF.
Hope this helps.