If you want a more pronounced reflection you could select a different custom reflection environment. You could try for instance the gem studio environment.
Placing the glass in an environment would be even better. There isn’t proper ray control for objects available in Rhino, otherwise you could add objects to the scene that’d be invisible to camera rays, but would show up through transparent objects and/or in glossy reflections.
Until such day you could try using a well-chosen wallpaper as background in which you’d place your glass.