I've always assumed that Sangaku Jime was just Japanese for Triangle Choke, as Juji Gatame is for Arm Bar. Or is the Judo technique opposed to looking the foot under the knee?
I can't imagine that there is much pressure on that bottom picture where the guy is tapping. Especially with his leg accross the shoulder instead of the neck. If you want to create big pressure to really put their lights out you need to pull the arm across, pull the head down, or both.
Edit: I mistook the Sangaku with Sankaku... Anybody know the difference (if any)?