The sweet spot isn't a spot, it's a range, albeit a rather small one. That's probably why you don't notice a difference if you go up or down a tad from the mid-range that seems to work best for you.
At the extremes, a twist or two of the string one way or the other will be noticeable. However, if you're in the middle to begin with, (i.e.,what works best for you, not necessarily the middle of the builder's suggested range) a twist or two won't be noticeable.
If your bow is quiet, doesn't vibrate excessively, etc., you're there. Just have to develop the confidence that you are and stop worrying about it. Good luck.