I'm a bjj noobie and today when i was live rolling with a 3? stripe, I took his back and crossed my legs instead of hooking the legs in an attempt to get a body triangle. After the session, he let me know it was a good way to get leg locked and also told me even a full body triangle is bad. I dont know if he meant for the same reason as just intertwining my legs; it seems a full on triangle would be too secure. Is there anything weak about riding the back position with a deep triangle?