There was no proper HiDPI support in Java 8.
In Java 9, JavaFx applications correctly scale to the monitor they are in. For example
if needed, found another couple of helpful JVM parameters from that website :
-Dsun.java2d.uiScale.enabled=false -Dsun.java2d.win.uiScaleX=1.0 -Dsun.java2d.win.uiScaleY=1.0