Bugger about the elbow, I had a fall about three months ago now and pretty much broke/smashed the elbow. Surgeon sent me to a physio/Occ therapist in Malvern.
They pretty much got me moving the elbow straight after surgery. Was told that the elbow only moves one direction so could only concentrate on arm extension and also bending towards shoulder. Can't say I spent much time with them directly more "under supervision" as they gave me exercises to do at home. Like you I don't think I'll get full extension again but I'm pretty happy with progress so far, and hope to get more when the plate is removed. Due for another check in with them on Friday and I suspect it will be the last until next year.
I'm glad I had a good level of fitness at the time of the fall as I'm convinced it has helped with the rehab. Strongly recommend that you do whatever exercises they tell you do at home. I heard lots of their other patients with excuses as to why they didn't do them and then surprised of their lack of mobility. Good luck with your rehab but sounds like you are determined to improve flexibility so you'll be ok