I would hope a 6" dragon would eat at least 20 3/8" crickets at each feeding with 2 feedings per day.
Regarding the reflection. I would cover the 3 sides with something patterned to hide some of the reflection. The backgrounds you get from pet stores work well for this. Reflections are dramatic when the light inside the terrarium is greater than the light outside the terrarium. Think of how much reflection you see in a window looking out at night vs. during the day. Try increasing the room light so he sees less reflection. He most likely thinks his reflection is another dragon. I would never even consider covering 4 sides. That would be like a funhouse of reflections.
My biggest suggestion is to get him on a very regular schedule. Two feedings of bugs per day with salad in between. Make the feeding times consistant. In the morning put crickets in and wait 20 minutes then collect all the uneaten crickets. Then do this again at night. He will get used to eating when the food is there and will eat better overall. Plus crickets left in the enclosure will eat anything including feces, bark, skin, your dragon, etc. which will make them unheathy for your dragon to eat and wandering crickets could be stressing him.
If you make a change stick with it. When I get sick dragons or babies in it often takes 10 days for them to get comfortable with the routine. But they always do.