[NikkiA]

The point of a 12-char short string is that it fits, with the size, into a 16byte cache unit and a single memory transfer on current architectures. Anything else will involve some loss of performance.

As for short strings, they don't have a prefix at all - the 12 bytes simply follow the 4 bytes of the length.

Long strings will need the pointer 64bit aligned, so a 4 byte length means you'd have 4 bytes wasted to the pointer alignment anyway, and you fill those with the preview 'prefix'. dword length + 4 bytes + 64bit address = 16 bytes, again. They both occupy the same space in the cache, and only the data at the other end of a pointer on long strings gets pulled into cache if you decide the prefix matches and you need to follow it.