Question on Unisons/Voices (Section 14 of Syntorial)

Question regarding Unisons, if anyone can assist. Here's what I don't quite understand:

When Unison Voices is on 2, why is it that the sound is the same regardless of (a) I only have Osc 1 on and (b) when I have both Osc 1 and Osc 2 on?

Shouldn't having both Osc 1 and Osc 2 on sound like 4 voices (since Unison has 2 voices, multiplied by 2 Oscs?)

Ditto for when Unison Voices is on 4. The sound is the same whether I have one or both oscillators on.

What am I missing about "voices"?