Rotate the dish so that the LNB moves 1 cm to the east BBC will improve.I think the chimney is the best spot. There aren't any great spots in the garden and there are the aesthetics of having a dish sitting in the garden.
So, today I went up and put on the new LNB with the existing dish. I got some nice improvements. I still need a new dish but got most channels but not much HD. BBC non HD was breaking up a bit. Channel 5 HD came in with good strength and normal quality on signal level screen.
The 125cm Gibertini really delivers what it promises, on antennas other than size, real performance depends on it later.A couple of points : It may be worth trying an Inverto Black Ultra instead of the existing LNB. This will allow you to experiment with the LNB to dish centre distance, due to it's extended neck. Also, is the dish mounted directly to the chimney stack or to your terrestrial aerial mount? If you did want to go up a size or two with the dish, how it is mounted is a major consideration.
Depends where you are in Spain.I have heard of people in Spain being able to pull in the UK beam channels with a 2.4m dish but that was a while ago so may be out of date now.