MFJ-932 vs Moonraker Whizz Loop

I've been playing with a Moonraker Whizz Loop for a while. Nothing I've been doing is fully scientific but it seems that the supplied loop is too small for 20m. Not really a surprise and my results really improved when I attached a larger wire loop (approx 3m vs 1.4m supplied). But using a loop using rg58u or rg213u did not seem to improve things further. I swapped to a MFJ-932 loop tuner and I expected an improvement but experience so far suggests the Whizz Loop is better.