The JavaFX packager determines the install target directory based on the vendor name specified for creating the package. The application name is used as the name for the shortcut to your application.
I assume you are using the JavaFX ant task to create the installer. In that case, you would have a build target setting up the FX task like this:
<fx:deploy ... >
<fx:application name="${application.title}" mainClass="..." />
<fx:info title="${application.title}" vendor="${application.vendor}" />
[...]
</fx:deploy>
In that case, you would need to set the ${application.vendor}
property to whatever you want as the target directory.