One of the things the map doesn't take into effect is terrain. If the explosion is on the other side of a large hill, it will shield you from the initial radiation burst and thermal flash, and any pressure damage will be reduced & delayed by having to go around or over.
You can set them for detonating at a certain altitude which might clear some terrain, true. You could also set it for a ground detonation where terrain will have more of a protective effect from the initial blast, but then there will be additional fallout. The prevailing winds will determine how affected you will be by that.
