Using the trade value chart, our pick is worth 1050 points, so to trade back to the 28th pick would be 660 points and their 3rd would be another 132points equalling 792. The difference is 258 points which equals another top 5 3rd round pick. If Atlanta would give up their 2nd round pick they still would be short, 960points which equals at least another 4th round pick. This is not law but why give our pick away for cheap, we would be selling our team short when we're suppose to be maximizing the draft.
A trade back for anything less then a 2nd would be a mistake in my books.