Yes, indeed. Just shows how sensitive the sat is.
I decided to conduct some real-world tests here after getting very poor results with the dual-band feed on my offset TV dish I use for the downlink, compared with the 2.4GHz wifi dish I was already using.
To my surprise, I found that placing a 2.4GHz feed just above the LNB is only marginally worse (1-2dB) than placing it in the focus.
Tested feeds were a single band LHCP patch, a bi-quad and a can (sorry, circular waveguide) with 1/4 wave probe.
The LNB was left in place and the 2.4GHz antenna held above it while transmitting a carrier and measuring the strength of the return signal on the downlink. The signal was also peaked by moving the feed towards or away from the dish.
The single band 2.4GHz patch came out best of course, slightly better than the wifi dish, but even the can was only a few dB down.
It’s very easy to try. It helps that the wavelength at 2.4GHz is more than 4 times the wavelength at 10GHz, so everything is at least 4 times less critical. Placing the 2.4GHz feed at the side of the LNB wasn’t so effective, so it is obviously a property of offset dishes.
The patch is getting waterproofed and mounted on the downlink dish when the weather permits.