BM, basically what Shockwave is saying is the Imax/A99 are a different kettle of fish when it comes to radials. There may be others that are similar, but these two are unique. The 1/2 wave is unique relative to the 1/4 wave and the 5/8 wave, radials will not respond the same in each case. Remember the discussions with Bob85 and his experiences with his Vector 4000, yet another entirely different situation concerning radials. So there is no simple answer regarding the use of radials.
Do you wonder how or why the Ringo and the A99 are said to work fine without radials and your 5/8 wave and my Marconi 1/4 wave will not work so good without radials? 
They are each different.
The Ringo and the Maco V58 are similar except for the radials on the Maco. I'm curious as to why the simple Ringo is not made or used much any more, do you know why?
You show images of the Ringo and the Wolf antennas. I have a Wolf 50_11m. It has design flaws and in addition it changes match whenever I raise or lower the antenna just a couple of feet. At best it operates with the best tune showing <>1.7:1 SWR. That does depend on height a bit, with being lower to Earth showing a better match, but all of this would really rankle most CB'rs today.
Maybe this is why these two are not so popular anymore---if they ever were. To be honest, I think both the Ringo and the Wolf are best used close to the Earth, and since they both are 10/11 meter antennas, experience tells us that low heights are no-way-no.
So, if you are interested in the effects of radials on your 5/8 wave, why are we discussing 1/2 wave antennas.
They are each different.
Again, it is just like Shockwave says, "...you can't have it both ways." The term "radials" is truly a generic term, but when it comes to understanding how they work on a particular wavelength radiator, you must consider that each of these radiators are unique with different magnitudes of current flowing in the typical areas around where the radials are attached. Radials are generally located in high current areas like in the 1/4 wave radiator, or with modest current flowing areas as in the 5/8 wave radiator a bit high of the base, or in areas with very little current flow as in the end fed 1/2 wave radiator.
These are differences that must be considered.
