There is many explanations of the anatomy and it depends on who you believe.
Personally I go for the true cubital tunnel being the area distal to the medial epicondyle where the nerve is between the ulnar and humeral heads of FCU. This area of the tunnel is covered by an Osborne fascia and if it has a thick ligamentous edge to it, as it often does this is the Osborne ligament. This area can also be called the Arcuate ligament, however I don’t use this term.
The area between the medial epicondyle and the olecranon of the ulna is the retro-epicondylar groove, although I am sure most of us just call it the cubital tunnel. In fact I think many of us just call the whole lot the cubital tunnel ! Which I don’t really mind. Then the bit proximal to that where the ulnar nerve sits on the medial head of triceps is often called Struthers canal. Struthers was one of those old while men in a grey suit who called all sorts of useless stuff after himself 🤣.
Clearly compensating for something!
So from distal to proximal I go cubital tunnel covered by Osborne fascia , ligament or anconeus epitrochlearis, then retro-epicondylar groove, then Struthers canal.
Or we can just call it all the cubital tunnel and describe the roof architecture (I am probably most happy doing this).