I guess it depends, some like the 1/6 and 2/5 nodes are a bit in front of the fret. But in the case of the 3rd position you can vary between 1/6 and 1/7 node on either side of the fret marker. Gives you either the 5th or flat 7th of the open string.
I don't go for anything that I have a high likelihood of missing. That's the way I've mapped them.