I've been trying to work on my left-hand positioning lately. Specifically, I've been trying to change from 'thumb-over' to a more balanced style with the thumb in the middle of neck so I can use my pinky more and expand my reach. However, when I play, I end up slowly sliding my thumb up the back of the neck into 'thumb-over' style. Any advice on keeping my thumb down? When I do end up keeping it down in the middle of the neck, it ends up bending backwards since I'm pushing so hard!
keep practicing, i had the sme problem, now my thumb always rests in the middle of the neck
Yep keep practising. I haven't had the 'thumb-over' problem but I do have a stiff one!

When I play scale my thumb doesn't move and my tutor has told me to relax my thumb and as I start to reach for the low E string then gradually move my thumb to the bottom of the back of the neck.

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