As shown in the last clip, starting in 4th position or higher gives stability to your hand frame. When we move to 1st position we need to keep the wrist in a straight line between hand and forearm, to allow it to be flexible and free. The wrist should not be pushed out or collapsed inward.
Be aware that in 1st position the intervals between notes are slightly wider than in 4th position, so you could need more backward stretch of the 1st and 2nd fingers to be in tune.
Have a soft contact between the first (index) finger and the violin neck as you move into lower positions. There is a double contact of the thumb and the inside of the first finger touching the violin neck.
SEE
Resources - Bibliography
Principles of Violn Playing & Teaching by Ivan Galamanian, pp.15 & 21
Scores - Start in 1st Position - violin & viola
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