Time and Angle. Tactics – plain and simple.
If you move the opponent well behind the baseline – you will have more time to respond, and their angle of play becomes smaller.
If that opponent is as deep but in one corner or the other, their angle remains the same but their cross court shot will cross the sideline at a steeper angle.
The famous Jack Kramer was known to play the ball deep and up the middle, whenever he had not gained control of the point with his serve or volley.
The same will work for you.
If you want more length and less effort on your forehand – check out STREAMLINING – using the template of an overhand throwing motion see how your legs, hips, torso, and even your non dominant throwing arm unlock a flowing streamlined forehand – REALLY