It cannot be overstated how important the middle of the foot is in the press, even (or especially) in the start position. If your balance is on your heels, your bounce won't be nearly as effective, efficient, or seamless, and your bar will feel heavier, move slower, and probably never make it to lockout in the reps that matter. I recently made the very simple and small change of centering my balance over the middle of the foot and my presses have gone from complete shit these past weeks to back on track immediately. A detail I hope never to forget.