And furthermore - try this excercise: describe a chocolate digestive. You might say, for example, 'a digestive with chocolate on top', or 'a digestive with a chocolate covering' (note a 'covering' would typically refer to something on or on top of something; the upper or outermost part; the part that is seen). You certainly wouldn't say 'a digestive with chocolate underneath', or 'a thin disc of chocolate with a digestive on top'. Clearly the chocolate is on top!
Or, alternatively, you might say 'it's a ****ing chocolate biscuit, get away from me. What is wrong with you, you nutbar?'