Kata-Gatame/ Head and arm choke/ Arm Traingle choke is used as a hold down in Judo, and it is mostly used as a choke in Brazilian Jiu-Jitsu and mixed martial arts.
There are many schools of thought regarding the best positioning for the top attacking partner. Some advocate laying flat on the ground with the hips low. Others prefer turning to a 90 degree angle, while others like to put a knee on the ground and drive forward.
Renzo shows some game changing adjustments for the Katagatame. He calls it the KatagaRenzo.
Important points that Renzo stresses in his version are hand placement, putting pressure, and not putting your weight low.
Here is Renzo Gracie demonstrating the technique on Demian Maia: