When we play a half-step (semitone) between the 3rd and 4th finger in high positions we have to be careful that the 4th finger is not sharp.
Also, if you anchor the thumb at the throat, the fingers become increasingly sloped as you go higher up the fingerboard and you need to take care that the 4th finger does not slip off the right-hand side of the fingerboard.
Practicing the finger interchange helps improve control of the 3rd and 4th fingers in high positions....
