After putting in a chunk of time in Cross-Sides Top would say the ‘fundamental’ to drill are mobile hips that roll around frames, sticky at the point of contact absorbing and nullifying bridging and shrimping through the legs:
From 3:10 on:
0:01-2:35:
The related new idea is, to the degree we’re loose, sensitive, and sticky with our hips, letting them do the dominating, we’re free to be equally loose with our hands and arms.
Ryron Gracie being water my friend via loose arms as applied to Cross-Chokes from Mount @ 15:32-16:10:
Credits: Xande Ribeiro, Rickson Gracie, Ryron Gracie
May the Force be Jiu-Jitsu: Philosophies, Principles, & Mechanics 