Congratulations on the successful experimentation. :up
I don't think the focal length would change because the parabolic shape wasn't altered. just extended. The F/D setting of the scalar would change if the added area conforms to the parabola of the dish. If this hasn't been readjusted, I think the added panels may be attenuating noise, more than adding signal to the feed. Or both, signal increase and attenuation of terrestrial noise. BITD i remember seeing in one of the satellite magazines, panels that looked very similar to what you've done here, advertised for combating terrestrial noise. Either way Better C/N ratio, and getting higher Q. This also brings to mind a question I've had for a while. That hole in the bottom center, of the dish, would also allow terrestrial noise into the feed, as the feed is aimed right at it. May see some C/N improvement if it were covered also. Don't know for sure, just a thought.