Ah ha!
Your reply confused me until I realised that I downloaded v2.0 rather than v2.1. The new version is a massive improvement on an already excellent piece of software.
This is working much better now.
I wonder, is there a way to detect (e.g. with another keystroke) that the position is back below the threshold (i.e. that the head is in the centre)?
Cheers,
Ally