Your posture is determined by your arm swing. If you swing up and down on a two plane swing then you should stand more upright. If you swing your arms around on a one plane swing then stand more bent over on the balls of your feet.
Get a perfect backswing every time with this four step drill, just raise the club up, then turn, then raise your hands and arms up and swing, it is as easy as one, two, three, four
Having the ball positioned too far forward in your stance can result in a high ball trajectory