Using "was" vs "were" for "as if"

For hypothetical situations, I've read that mostly, it is safer to use "were" for ifs.

If the world were peaceful, there would be no wars.

But, I've also read that for some unhypothetical/past situations, it is correct to use "was".

If he was here, he would have gotten perfect.

That's indicating the past, not the future. "If he were here" conveys a slightly different meaning I believe.

Though it is understandable, it is still quite a blurry line, especially when "as if" comes into place, which is my original question:

For "as if" circumstances, like the one below, is "was" or "were" more appropriate?

He gazed upon the massacre before him with tranquil eyes, as if he was/were a spectator unrelated to it all.

The above does seem to be somewhat hypothetical, so "were" would seem to be the correct answer. However, it also seems like a comparison, as it is comparing a spectator to him.

So, question: For "as if" cases, should you always use "were", and if not, in what situations should "was" be used?

"Were" is used for subjunctive mood: when the condition is contrary to reality. (And some other cases not relevant here; see the Wikipedia link at the end of this post.) Examples: if I were you (I'm not); wish you were here (you're not); if I were rich (I'm not); as if I were an unaffected spectator (I'm not).

But sometimes the condition is not known to be contrary to reality. "If the killer was hiding in the shadow, he could easily have come from behind": we don't know where he was, he may have been hiding in the shadow, so we say "was" not "is" simply because we're describing the past. "I don't know if she was aware of that. If she was, she should have said something": maybe she was, maybe she wasn't. So we say "was" not "were."

There's more on this from Grammar Girl, and from Wikipedia.