grammar - Determining if "than" is used as conjunction or preposition

"than" can be used as a conjunction and as a preposition. I want to be able to tell for any given sentence containing "than" which grammatical function it has in that sentence.

My current understanding is as follows:

1. When "than" connects two clauses or phrases it's a conjunction. Examples: We shouldn't spend more than we earn. He's taller than I am.



2. This also applies when the second clause or phrase is elliptical: He's taller than I.


3. But when "than" occurs with a pronoun in the objective case, it's a preposition: He's taller than me.


4. It's also a preposition when numbers/amounts are compared: It takes less than an hour. A crowd of more than 10,000 had gathered.

Is this correct so far?

I'm confused about the following:

But aren't these all elliptical sentences (e.g. I'm taller than my dad is), and hence all cases of "than" as conjunction?

My question has a practical background: I want to apply proper title case to a number of song titles. According to both the Chicago Manual of Style and the Wikipedia Manual of Style, four-letter prepositions are not capitalized while (subordinating) conjunctions are capitalized, so I need to be able to make the distinction.