Your wrist is far too bent. Holding it in flexion like that will create needless tension.
Straightening it (see pic of Jaco above... wrist straight but fingers bent) will make lots of what @Mushroo advises fall into place naturally.
You may also use the Segovia style wrist (wrist still straight, but elbow and instrument in different position to body). Lots of pics of this.
Bottom line is that extensor tendons of hand won't like a wrist in constant flexion and your fingers will tend to bunch up.
Thanks, will try to straighten things out. Can see a slow couple of weeks of reprogramming coming up.
Thanks for the video, but that exercise is the one I explained in the OP. It's helped my ring ad little finger, but as it was hving little effect on the middle finger I was looking for an alternative. Thanks for taking the time though