You seem to think that there are places on Earth where such protection is likely. Since the blast is 2000+ feet up, your map is not even close to being accurate. However, if there are actually mountains in the way of a blast, protection from the blast is certainly a possibility for A and B. Fallout though becomes a massive problem. The blast will strike the edges of the mountain and spray it out all over the other side. This is a very strange argument where you seem to think that there are places to stand when a nuclear bomb goes off.
No. Do you think there are places anywhere near you with Mountains over 2000+ feet either side? If they are domed elevations, this can potentially work against the protection. Do you think there will be just the one blast? Surely you don't. Even just one of their SS-25 weapons would devastate London. Hiroshima was 15 kilotons, an ss-25 is 550 kilotons - that is 37 times more destructive force for just one missile. If you think huddling up next to a Mountain is going to work, then best of luck to you. I'd rather be right underneath it.
Nuke tests - I already said these are carried out mainly at sea level or below so I never made that claim. Mountains would stop the blast at low level.