Yes, SR-71 flew at 20km height, so at the moment of launch, target was at the end of zone 3. I do not talk about probability of hit - the missiles were lost from almost very beginning, they were guided to a jamming signal but they went completely off the correct route.

It's a pity I haven't observed KRO signals, will try it again. And I noticed on the second page of this thread that I am not only one who faced this problem.