A follower sent a clip from bottom side control. Their forearm was across the passer, but the elbow floated away from the ribs. The shape looked correct; the structure was not connected.
A frame only works when the force reaches the floor through your skeleton. With the elbow floating, every ounce of pressure was absorbed by the shoulder.
Bring the elbow home, angle the forearm toward the near shoulder, and move your hips while the frame preserves distance.