arm in side choke from side control

i have uke in side control and he secures an underhook (his right arm). he then tries to turn into me up on all fours. i use one hand to feed his lapel to my other hand so that the more he turns into me the tighter it gets. i use my other hand to grab the other collar and pull uke into me as if i am going to pull guard. but only one leg ends up on top of him as i end up on my side. my leg is there to keep him from jumping over me to escape the choke. this choke requires no precision on the grips and is remarkably tight. one key is to keep my elbows close to my body.