You won't see any downward radiation in EZNEC with the antenna this close to the ground. Try it in free space. When I did it 36 feet over real ground and shortened the radials a little, I could see an increase in radiation directly upwards by 3 db. When you're in free space you will notice that the radials above the beam cause the pattern to tilt.
Depending on the length and location of the radials you can tilt the front lobe up while pulling the rear lobe down or vise versa. That's because the parasitic elements the radials make up are not in the same horizontal plane as the beam. The current you see exciting the radials will now skew the pattern so that it's tilted. This same effect occurs when vertically stacking elements if they are not all in the same vertical plane.
Well guys Shockwave is exactly right, and this is why we might have missed completely what he was getting at.
Here is my model (Yagi 2- SP500 above 108") in free space, and it does show what is said.
I realize you guys might not get much out of Free Space models and complain sometimes, but it requires a different perspective to appreciate how they can be important. They do demonstrate much better how antennas or affected by their construction, the mast, and their location relative to Earth like SW said, and what is close by if any other thing in included in the model.
By removing these losses from the model, we see a much better picture of the true nature of the design. Of course the Earth and the stuff on the surface changes what happens, but we do need to consider FS ideas before we build the design, and then later we can test in the real world. Does this make any sense for why we need FS models in modeling?
View attachment Shockwave's idea in free space.pdf
Wire Dawg, I can't specifically answer your concerns, but there would be some differences. However, I think the basic results would be about the same. One thing going on here might be cancellation effects that have not been discussed, and that could come into play with the model over real Earth, but that is just a guess on my part.
My antenna experiment years ago with a Starduster that have radials about 7'+ hanging down below the hub, was mounted on a 9' mast above my 4 element horizontal yagi...and I detected NO differences just using my radio. When we put our antennas over real Earth...things are a bit different it seems.
Good luck and keep us posted.
I forgot to add the model of the Yagi 2 by itself in Free Space and you can see for sure the GP is the cause of the pattern difference.
View attachment SW's idea without the GP antenna..pdf