Carrying Capacity and multipliers

Question

I have a character that's Large and has a Belt of Wide Earth. Large size characters have a carrying capacity twice as good as Medium size characters, and the Belt doubles the carrying capacity of the wearer.

• If I were to treat both as multipliers (after all, this paragraph uses a X2 notation), my character would get thrice the carrying capacity of a Medium character with the same strength score.
• If the doubled load of a Large character was a sort of entry in a table instead (meaning that the base carrying capacity of a Large character just happens to be two times as big than a Medium character, but no actual moltiplication is involved), this character would be able to lift four times the weight a Medium character can.

While the question is "what's the right one?", I need you to break it down this way:

1. Is there an indisputable, by-the-rules, "right" option between those?
2. If 1 is not true, is there any semi-official answer, like a FAQ or Sage answers?
3. If 1 is not true, what is the community consensus, e.g. in the optimization forums? I know this to be the foundation of the Hulking Hurler TO build so I'm quite sure there's some kind of consensus. If it's debated even there, please say so.

I'm going to use this for a TO challenge where I try to one-shot the Tarrasque with a 78k XP character, so I need to get the most official source on the matter. I will ask for deletion of any answer that does not start from 1. down

(TO = theoretical optimization)

Answer 1

Your carrying capacity is four times that of a medium creature, not just three times.

Only "abstract" numbers (modifiers and die rolls) use the special multiplier-handling rules, while concrete quantities such as weight use normal math. This is unambiguously covered by the second paragraph of the multiplier rules:

When applying multipliers to real-world values (such as weight or distance), normal rules of math apply instead.