Hm... i understand what you mean... indeed, the absorption of the THC by the cheese only happens in its surface, and thats why its said to grind the weed as fine as possible, to maximize the surface of contact between them.
Of course, "bathing" the weed with oil will produce far better results, since the people have time (and pacience) enough...
When i make weed sandwich, i use hash oil instead weed, and i spread it through all the slice of cheese, until it form a very thin layer... so, when the cheese melts, the hash oil mixs with the cheese and the cheese becomes greenish... in this case, the absortion is greater, and the amounts of hash oil required are smaller.