It doesn't, there's no singular optimal amount of over-provisioning. And that would make no sense, you'd have 28% over-provisioning for a 100/128GB drive, vs 6% over-provisioning for a 500/512GB drive, vs. 1.2% over-provisioning for a 1000/1024GB drive.

It's easy to find some that are marketed as 500GB and have 500x10^9 bytes [0]. But all the NVMe's that I can find that are marketed as 512GB have 512x10^9 bytes[1], neither 500x10^9 bytes nor 2^39 bytes. I cannot find any that are labeled "1TB" and actually have 1 Tebibyte. Even "960GB" enterprise SSD's are measured in base-10 gigabytes[2].

0: https://download.semiconductor.samsung.com/resources/data-sh...

1: https://download.semiconductor.samsung.com/resources/data-sh...

2: https://image.semiconductor.samsung.com/resources/data-sheet...

(Why are these all Samsung? Because I couldn't find any other datasheets that explicitly call out how they define a GB/TB)