I have seen the S-mount used to transition from front chokes/RNC's to shoulder locks, if the opponent tries to spin out from under you. Good position that I don't use often enough. Hadn't considered using it when they try to upa me, but I'll give it a shot next time. Thanks!
_________________________
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin