I have only ever studied Simandl and after 4th position he indicates the thumb should move from the back of the bass to the side, but there are often cases in the music where it seems more advantageous to pull it to the side earlier or later. I have attempted pivoting as suggesting by advocates of the Rabbath method and can certainly see the advantage of this playing in these positions, however without a proper teacher I am concerned that this will not benefit my playing. To that point, I tend to experience discomfort when ascending this way and what should be a comfortable part of the bass becomes uncomfortable. I would like to get your thoughts on approaching this area of the bass. Shifting, Pivoting and a few exercises to maximize relaxation and agility in this area. Thank you for your help.