Starting out - either 3 under or split finger - there is a lot of aimin' goin' on.
As one develops a disciplined shot sequence, builds muscle memory, and practices shooting at different distances, the aimin' part "seems" to go away for many shooters so that they become instinctive (unless they train themselves to use the tip of their arra, etc.).
It has been almost a year since I switched from RH to LH shootin' and when I made the switch, I went with 3 under. After trying multiple different anchor points I settled on the one that was most comfortable for me and started groovin' the shot.
Surprisingly, even though I am right-eye dominant, my LH shooting after 10 months is better than it was after 30+ years of RH shootin'.
I should mention that I have shot 18,000+ arras left handed since I made the switch....
Develop good form and then practice, practice, practice. If your form is not good, it won't matter how much you practice.
Shoot straight, Shinken