Hi Iain,
do I understand correctly that you’re using the PC as a giant eye tracker, with an app running on it acting as a proxy, and the UI on the Android device?
In that case I would recommend using the Gaze SDK rather than the EyeX SDK. It gives you full control over display area configuration and calibration — which makes sense for this use case. There are calibration code samples written in C++/wxWidgets and C#/WPF (sorry, no Java, but it should give you an idea).