For many violists and violinists playing beyond the third position is challenging because it feels like such a ‘reach’. But think about it, if one were to try bringing the arm around without the instrument, to touch one’s nose with the index finger, for example, which is actually a greater distance than playing in the 10th position, it is effortless. It is easy to touch ones finger to ones nose.
One may ultimately find the culprit is excessive elevation of the shoulder along with tightness in the upper arm. If the player is not ‘balancing’ the violin or viola then he is most certainly gripping it or creating a ‘C’ with shoulder and tilt of head to the left, so instrument feels secure.
Try the same simple motion of touching ones hand to the nose, then squeeze the left shoulder to the ear and notice how much more of a strain it is to touch ones nose.