Thanks for the reply. Please could you clarify what exactly you mean by 'a diagonal movement'? I'm sure you understand exactly the movement you would use, and I'd get it straight away if you demonstrated. But in the absence of this possibility....
Anyway, are you using fingers 1-4, 2-5? Next, do you mean that the hand stays still relative to the forearm? To get the diagonal movement you must be moving your hand to the right, but do you move in or out of the keyboard? Finally, is your hand stretched out Ab to Ab or are you making the reach by (rapid) lateral movement of the hand?
Sorry for all the questions. Thanks for your help.
Richard.