I have come to the conclusion that my large(1 meter diameter) spiral loaded vertical is really an asymmetric dipole with the spiral being the other radiating element. For fun I made a much physically smaller spiral and attempted to use that.
New Small Spiral
I found it was extremely difficult to tune and narrow band as well. It did work but the receive level went down slightly so I have concluded it is not as efficient as the large spiral. Feedpoint impedance measurements were better matched(higher R) than the other spiral but this is surely IR loses in the dense coil.
My conclusion is a moderately sized spiral of a few turns(> 1/20 wavelength) is very effective as its area makes it a respectable radiator. If the spiral coil becomes small the approach doesn’t work so well. My large spiral is a solid performer and it is my opinion that it is preferable to a modest radial array.