You must not have read that link at all, because it also explains that many of Sprints towers have equipment that is incompatible with circuit switch fallback, so Sprint customers on Tri-band phones ARE experiencing the inability to receive calls when they are on LTE. It also explains that once Sprint completes it's network upgrade, the incompatible equipment should have been replaced.
It was a pretty helpful link, much more helpful than claiming that the right answer is the wrong answer. Good read. Try it.