I'm a little confused as to how Plone handles images sizes. For example, in Site Setup > Image Handling I have set the "Large" image size to be 700 px:
That's a hardcoded in the JS File of the TinyMCE-Pattern. But i don't know really how to change this. A Plone JS Hero is needed! Or a good tutorial how to customize the pattern. In principle its a ajax call to a BrowserView that returned the registry values of allowed_image_scales.