Starting in 4th position or higher allows you to rest the palm of the hand against the body of the instrument. This gives stability to your hand frame and helps avoid pushing out or collapsing in of the wrist.
In the higher positions because the hand contacts the violin we can release the contact of index finger against violin neck. This encourages an easy backward stretch of the 1st finger.
Tapping the finger with the open string in between helps develop the correct finger action. This type of (relatively) silent practice is also good since you are not distracted by bowing issues.
As shown here start with a very light fingerfall. That is, with enough finger contact with the string to hear the note, but barely pressing the string down in order to concentrate on the ease of finger drop and lift. Once the finger action is reliable then work on the more vigorous finger action needed to play with clear articulation.
Resources - Bibliography
Principles of Violin Playing & Teaching by Ivan Galamian, pp.15 & 21
Vioolmethodiek by Qui van Woerdekom, part 2, for Backward stretch
Scores - Start in 4th Position - violin & viola