doubling “so” to get half the effect

In the sentence, “I feel so bad,” the word “so” expresses the bad feeling to a greater extent. “So” is making what you say so much stronger.

But if you combine two “so”s next to each other they only express to a moderate extent.

“His leg is but so so.” Having two “so”s back to back makes something weaker, instead of stronger.

Maybe it’s the cutesiness of it. Like saying “poo poo.” Saying it twice softens the crudeness of it.

2*poo = 2/poo