I've been testing on 2 accounts, my main doing 38-6, and my alt doing 37-6,
There's no noticeable difference.
I calculated the difference 11 quests ago, and the max difference I got is 2, it is currently 1.
The number is a straight total crowns from 38-6 - total crowns from 37-6.
If the number is positive, 38-6 gives more, if it is negative, 37-6 gives more.
I am updating the numbers over here:
It is in Chinese, but the 5th row is the difference, and the 6th row is the number of quests each account finished.
Use google translate if you want to know what those other words are saying.