The blocked area labelled 1 covers the North Downs. This natural boundary lurks to the NE of me and I can’t do a great deal about it.
The blockage labelled 2 is, I believe, down to the aerial being inside my loft and the terrace houses of my block extending in that direction. I wrote about that here. The only way to improve this range would be to get the aerial placed above the roof of my house, which is not a job I am going to undertake. I may, however, consider getting someone else to do it.