Part of the problem with some receivers - and ham transceivers too - is that the sensitivity below 1 mhz is deliberately reduced (sometimes with a pot or resistor...) to reduce overloading issues. Depending on how the RF deck is designed, that might also hit the LW band as well.
Now that applies to LW beacons - there are many beacons on HF as well (outside of the usual ones found in the ham bands) that many assume are for propagation studies, although there have been other more unusual apps that have been suggested...best regards..Mike