Thanks Rick, I've been doing some reading and thinking about my tremolo and so far have come up with...
1) It would help if I used another camera angle so I can see what my RH fingers are doing (for tremolo and other pieces)
2) There are lots
of posts on the forum related to tremolo and the frustrations on achieving a smooth, fast tremolo. So far these have led to some interesting external pages/resources by Tom Poore, Douglas Niedt, Philip Hii etc.
3) The little work I have done in the past (an infrequently undertaken exercise from Pumping Nylon) has been focussed around control and planting. This might be very useful at some stage of development or for some people, but I think
Tom Poore is on to something when he suggests at http://www.pooretom.com/learningtremolo1.html
to 'start with speed and gradually add control'
4) I should also not get hung up on aiming for pami; instead seeing what works for me
5) The 'thumb swatting' that Douglas Niedt describes struck a chord too, as did the advice about working on the second string for tremolo to help minimise the RH finger movement
6) It will take time....