I'd say those criteria are sufficiently broad. I'll admit, shooting someone in the back creates questions as to the intruder's intent. In a split second decision, it's very possible that the intruder seemed threatening, or didn't. He may have been facing the homeowner seconds earlier. I wasn't there, and neither were you. 

Note that the LAW emphasizes broad terms such as "might" and "no matter how slight". I'd say this puts the burden of proof on the prosecution, and it won't be easy. It shouldn't be. The guy should be able to defend his home and family.