Its position is the key to the kite's flying performance and behavior. Most deltas use a towing point that gives as much lift as possible while retaining good handling - that is, it could be shifted further aft for even more lift, but the kite would become reluctant to climb while it's at a low angle. It's a case of maximizing pull and responsiveness together.
Conversely, reducing the kite's efficiency by shifting the towing point forward isn't necessarily a bad thing. You lose lift, so the kite doesn't pull as hard, but it can then fly in much stronger winds than would otherwise be possible with a normal light wind towing point. However, stability deteriorates dramatically as the towing point moves forward, and this makes strong wind deltas rather difficult to design.