Contour is the working principle of body-to-body technique: the contact surface is shaped to follow the curves of the client's body rather than pressing across them flat.
A palm is small and flexible. It fits a shoulder blade without effort. A forearm is straight, a torso is broad, a thigh is rounded; none of them fits a human back by default. Contour is the skill of making a large, fairly stiff surface follow a curved one.
The difficult terrain is predictable. The hollow of the lower back, where a broad surface bridges the gap and touches nothing. The ridge of the spine, which a heavy pass should run beside rather than along. The shoulder blades, two raised plates with a channel between them. The back of the knee, soft, and passed lightly or not at all. The neck, too narrow for anything but a hand. A trained therapist maps this terrain in the opening minutes, usually with her hands, before the wider contact begins.
Angle, not force. Tilting a forearm lets its edge settle into a channel while the flat rides the higher ground. Bending at the hip lets a torso wrap around a shoulder. Weight shifted from one knee to the other moves pressure from one side of the spine to the other without any lift. Oil makes each of these corrections smooth; on dry skin every one would arrive as a small jolt.
Contour is the reason body-to-body suits bodies of every size and build. The technique does not demand a particular shape. It demands attention to the shape that is present, and that attention is what separates a practised therapist from someone who merely lies across a client.
Larger frames are discussed in the journal on tall or heavy guests, and full contact sets out the surface itself.