[PeterisP]

GPS spoofing is generally done at limited range and line of sight so the fact that "horizontal signal will suffer pretty fast" and having the range limited by terrain and curvature of the earth is not a problem but a feature that the spoofers generally want - affecting the target, but not affecting people 500 miles away; and sometimes even explicitly doing that from a pit so that spoofing or jamming affects airborne targets but not those on the ground.

And regarding "If you want to spoof GPS signal very well, it should be also weak" the scenarios I've seen (e.g. targeting drones in current conflicts) often explicitly target non-sophisticated commercial off-shelf GPS modules that don't attempt to detect spoofing and will gladly accept a signal that's 100 times louder than the actual satellites, so I think the spoofers often have no desire to do it "well" according to your criteria.