I've been messing around with the truss rod for the past couple months, trying to get the neck as straight as possible. Now it's straight, and I again noticed how high the action is. So I measured the distance between the top of the 12th fret and the bottom of the bass E string, and it's 4mm apart. How can I lower the string height? Should I try sanding down the saddle? Or should I just take it to get set up by a professional?