I think that's all correct too. But it raises an important point: the test is subjective - i.e. it doesn't matter if Pistorius' fears were objectively "reasonable" or not, only that they were genuinely held by him. However..... in assessing whether Pistorius can have genuinely held that fear (that his or Reeva's life was in imminent danger), it's still necessary - mandatory - to apply an objective test to that assessment.
To go back to an example I used some time ago: imagine if I was walking down Tottenham Court Road at 11am on a normal Friday, and a man of around 18 years old with a mohican haircut was walking towards me on the pavement. Imagine if I was carrying a concealed knife in my pocket. Imagine that as the mohican-guy approached me, he put his own hand into his pocket. Imagine that in reaction to this, I pulled the knife out of my pocket and stabbed the mohican guy to death.
Now imagine if I claimed as a defence that I genuinely believed that the mohican guy was reaching for a knife with which to stab me, and thus my actions were in self-defence and were proportionate to the threat I perceived. It simply wouldn't be acceptable for a court to say "Mr LJ says that he perceived an imminent threat to his life, and we've seen nothing to contradict this claim, so we therefore accept that his claim in this regard is genuine. He cannot be guilty of murder." In reality, some sort of test would have to be applied in order to determine whether my claim to feeling in imminent mortal danger was genuine. And that test would take into account the context, the time of day, the fact that I didn't know this person at all, the fact that there are plenty of similar-looking people walking around in London, all of whom I would have previously encountered in the street without incident, and the fact that people put their hands into their pockets all the time for entirely innocent reasons. In this particular example, I would expect the court to conclude either that I was lying about feeling in imminent mortal danger, or that I was mentally incapacitated at that time.
In addition to the above, if you stop to think about it, if it were that easy to "pass" the subjective test, then virtually everyone accused of murder could, with canny legal advice, claim that they genuinely felt their life to be in imminent mortal danger at the time they killed the victim. You're charged with murdering a gang rival? No problem! Simply claim you genuinely felt yourself to be in imminent danger of the other guy killing you, and hey presto! You can get it downgraded to manslaughter! You strangled your wife in the bedroom during an argument over your extramarital affair? No problem! You claim that your wife was moving towards a heavy brass lampstand in your bedroom, and that you genuinely thought she was about to grab it and strike you repeatedly over the head with it until you were dead! Hey presto! Manslaughter not murder!
The point is this: even though the test is subjective, there must still be an objective element to the assessment of whether the accused genuinely did (or could have) held those feelings at the time of the act. The court cannot simply say something along the lines of: "Well the accused claims he felt in danger, and we haven't heard anything to actively disprove his claims, therefore we must accept his claims as genuine and honestly held".