There's actually 5 basic and 5 advanced controls. There's a whole lot more in the entire osae komi waza syllabus, which are more or less variations on the same principles.
This topic was already dealt with in the pressure point forum, but I can't seem to find it. Ah well...
It's not actually a pressure point. It's somewhere on the radial nerve between LU6 and 7. In fact, if you understand the principle, yonkyo/yonkajo can be applied anywhere on an appendage.
Having said that. It's not a pressure point technique as such anyhow. If you don't get the te kubi shime and kuzushi right to begin with, forget about the point, coz you'll miss it - the point, that is - no pun intended.
All can say is more practice.