I think I understand now where my problem with the configuration is occurring, and I though I’d share.
I run Elite Dangerous on a laptop with a second screen attached.
I normally run an extended desktop with the laptop display as primary and additional screen as secondary, with Elite Dangerous displaying on the secondary in a borderless window.
By changing this to show the additional screen as primary and laptop built-in display as secondary, with Elite Dangerous displaying on the primary display, The EyeX is now working properly on both axes.
I guess there is some code inside the EyeX software package somewhere that got confused with my normal screen setup, and thought the I was gazing far to the side, instead at the centre of the screen?