> Maybe I'm missing something basic but that still doesn't explain why it's 30% and not 50%. It's like tipping. There's no ideal value that can be picked; just

> Maybe I'm missing something basic but that still doesn't explain why it's 30% and not 50%. It's like tipping. There's no ideal value that can be picked; just agreed normal values. If 30% appears to work most of the time then that's probably why it's used.