In this image our model "B" is demonstrating how she can change the angle of penetration by adjusting both the tilt of her pelvis and where she positions herself on top of A. This can impact the depth of penetration and also where she will feel the penetration most.
B can also change the way this position feels for A, who is on bottom. By moving herself further down towards A's legs, B will create more of a pull on A's penis (or strap on). This can increase the friction and stimulation for A.