Oops... again, I mis-pointed the dish (the previous instance was dish inside the room, pointed to 123 and assumed to be at 125 W).
As usual, vigilant forum members noticed it and thanks to them, correction could be made.
However, after moving the dish more to West (from 103 to 107.3 ) the distance between original LNBF assembly and sidecar LNBF has increased significantly.
This makes the whole idea not feasible (unless, some magic scalar with feed is invented for gathering all the dissipated "rays" resulting from far-off-axis position).
Another sub-topic, which has emerged, (modifying round LNBF to elliptical - or - panoramic - dish), is still worth pursuing, though.
More info on pictures (some annotated).
Oops, again, now there is a problem with uploading my files (photos)...
So, maybe later ...
Cheers, polgyver