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2.4GHz S band helix feeds, et al.

Hi, Everyone,
Does a helix feed for S band require a reflector?  The feed I ordered a while back from WiMo doesn't seem to be available any longer, so I cannot tell you what the model number is.  It is a plastic-sealed unit, about 5-6 inches long and has a diameter of about 3".  Is that a sufficient diameter to suggest that it does have a reflector at the base, just forward of the N-type female jack?
I have integrated this feed with my AIDC 3731 S band downconverter, purchased around the same time as the feed from Bob, K5GNA, and am thinking about how best to mount it to my DirecTV dish.  The IF rig and signal source I'm using to determine the focus and best orientation for the feed WRT the dish seem to work best together when the rig is listening in FM mode -- that seems to provide the best indication of the sweet spot when I wave the connected feed and DC in front of the dish, in the vicinity of where the DirecTV LNA/LNB would mount.  But the location of maximum signal pickup isn't quite in the same location as where I estimated the helix of the TV LNB/LNA would be.  Are there reasons for this?
I also have some large BBQ type dishes, one of which I was thinking about covering with aluminum screen and using instead if the DirecTV dish doesn't cut it.  Ultimately, I'm hoping this will all work on P3E S band.
Any advice would be great.  Am I missing anything here?
73, Ray KA8SYX
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