Organic Rotoscoping - harder than it looks!

Ok, so what am I doing wrong?

I grasp the principle of planar tracking and have seen the Dusty Springfield tutorial. I’m trying to roto the t-shirt of an actor in 3 secs of footage. There’s some slight movement and then a quarter turn.

I suspect I do this as one large shape, and realise that I can move the outer and inner points separately (am using a Bezier mask btw).

The track just doesn’t match the movement, or at least only about 80% of the mask does - movements on one part of the image are mainly tracking but some are going out and just not keeping up with the bigger movement on one plane as the actor turns.

I’ve enclosed the footage in the following RAR set (3 files):

During the shot the camera is locked off, so I shouldn’t have a need to worry about an adjust track - should there?

Any thoughts would be greatly appreciated.

Kind regards,