Looking at the model I was curious about above, here is why I think the difference might be happening.
[photo=medium]6395[/photo]
Here we see, immediately under the 8 shortened radials, we have currents that are nearly as strong and in phase with the top 1/2 wavelength of the antenna. These currents should act much like a collinear antenna, having a beneficial effect on the lower angle lobe.
There are still significant currents on the mast that are out of phase, but their strongest part is right next to the earth, which is having an attenuating effect on them. Another way of describing that is, ever work with a ground mounted antenna and test it as you add radials? As you add radials the antenna performs better and better. So for these out of phase currents near the earth think a ground mounted antenna with no radials...
A question that comes to mind is how are these currents as they are? Both sides of the feed point will normally have the same current phase and magnitude, so what is causing the difference here? I think the radials are not acting like a ground plane, but instead acting like a capacity hat. That is the only thing on the antenna I can think of that would cause this change in the current phase /magnitude instead of what I would normally expect to see in an antenna model.
I want to point out that what I am posting is my opinion, nothing more. If someone has a better explanation I would love to hear it.
I would like to look at this antenna at multiple heights as M0GVZ mentioned, but I don't have time right now so I will do that later.
The DB
