Not always true... try tuning the Icom 746 below 1600 khz and let me know what happens. ;-)
Well, I'm listening to 540 kHz right now, WFLA, on my Cushcraft R8 which has a bottom tuned frequency of 7mhz and 300' of coax.
They're coming in about 20 over S9 with the attenuation turned off.
That's what happens here.