I am a bass player of almost two years, and am a very proficient player. I try my hardest to fix my techniqe to improve my playing style, but I'm seriously questioning my left thumb. I suppose the proper way to position your fretting hand involves placing your thumb perpendicular to the neck, but I tend to keep mine either parallel or diagonal to it. It's normally only correct when I strech my fingers out. Although sometimes it sticks above the neck, it doesn't seem to affect my playing at all. I was just wondering if anyone does this, or if it even matters.
i do the same thing. i dont think you should focus all your attention on fixing this problem. if it really doesn't really affect your playing then there's no need to fix it.