Cousins V and Spike are truly Cello Lower-Bout-Contact Experts!
V would like to add his opinion, and also share his V-shape to reference these contact locations too!
The contact that the lower bouts make with your legs, added to the end-pin floor contact, form a large V-shape.
At this point you have learned two of the three main cello contact locations:
END-PIN/ROCK-STOP AND THE FLOOR — Knowledge accomplished
LOWER BOUTS AND YOUR KNEES — Knowledge accomplished
Hang on! You are almost there!