I am trying to find out if the term urogenital diaphragm is correct or if it is not proper terminology.

When we were working on Gray's Anatomy for Students, we actually spent considerable time sorting out exactly the questions you are asking about the "urogenital diaphragm" and the deep perineal pouch. From a clinical point of view, the term urogenital diaphragm is not used and it does not exist. Additionally, in the Terminologia Anatomica it is also not listed and in a foot note it is referred to as a misnomer. So in our text we have not used this term. It is appropriate to refer to the structures in this area as being in the deep perineal pouch. This pouch is closed inferiorly by the perineal membrane, but open superiorly. There are some differences of opinion on this point, but in most cases the inferior fascia of the pelvic diaphragm is not considered the superior fascia of the deep perineal pouch. Regarding the anterior recess of the ischioanal (ischiorectal) fossa, it is superior to the deep perineal pouch.

I hope this helps you get started on trying to define the location based on proximal landmarks.