I could be wrong; I didn't really hit grade 5 until 38 when I could track the nodes.

From 1.17 patch notes:
[dev1039] When the three below conditions are met in regards to the grade and difficulty of a gathering attempt, the "sweet spot" of the approach phase will be in a fixed location.

1. Class rank
2. Values of VIT for miners, STR for botanists, and DEX for fishers
3. Bait and lures (for fishing only)

ex.) At a certain grade and difficulty, having the appropriate rank, DEX value, and bait/lure will ensure that jigging the rod precisely in the middle will result in a black eel hit.