I agree optimal TX and RX antennas aren't necessarily the same. TX is all about e.r.p., while RX is all about S/N ratio. Some receiving antennas might be 20 dB down from TX antennas but if they improve S/N by even 1 dB, they're better. It's why people use Beverages, loops and all sorts of stuff you wouldn't want to transmit with on the lower bands. Sometimes if my noise level is high, I use my regular TX antenna and then use a separate RX antenna which might be terrible (like using my 20m beam on 80m) to improve S/N. On my 80m antenna a signal might be S9 but if noise level is also S9, it's hard to hear that signal. Using a lousy antenna (like the 20m beam on 80m) might reduce the signal to S1, but if noise level is S0, now I can hear that station just fine.