Energy is scattered from the edge of the reflector, causing both incident and reflected energy to spread spherically from this point. The wavefront is diffracted around the object, and some distance later the wavefront has 'healed' back to almost its original form, making it difficult to detect the object. Less than critical angle . Most of the wavefront penetrates the interface and is 'bent' according to Snell's law. A fraction of the wavefront is reflected.
Reflection is strong.
Greater than critical angle . Wave is completely reflected from the interface. Mulpile reflections are built up as it travels down the box.