There is also an experimental feature that allows you to use forward lighting in a material to get some better specular highlights in the reflection.
You will need to change the Translucency Lighting Mode to be Surface PerPixel in your Material. You will also need to enter the console command r.ForwardLighting 1 to enable this.
Here are some samples from my test level:
Surface PerPixel enabled:
Surface Translucency:
This is the area being reflected by the Box Reflection Capture I’m using:
Material values used for glass:
You’ll see the biggest gain in the glass reflection by using a higher value (0-1 range) for the Specular input.
Hopefully this can help you get your scene sorted out.