24 db gain only sounds possible as comparison to a severely mismatched antenna you are using to transmit. Like a high Z antenna connected to a low Z port.

I seem to recall now an item from a decades ago QST. It compared similar output power mobile radio distance on 160 and 80 meters. I seem to recall that 160 was clearly better, even tho the ant there was 1/2 the miniscule 80m wavelength fraction. Due to longer reach of groundwave, if i recall; even with the greater loss in the 160 loading coil. Thus i suppose, the reasoning for the WW2 German vehicle radios that operated in the 1- 3 MHz range, some even lower, such as their 100WS transmitter.