I guess amazon have done a cost analysis on their packaging – if they reduce their packaging, or carry several different types, this will costs more, both in having to stock, use, order and commission several different types, and also in terms of returned items that that been damaged due to inadequate packaging.
Now the financial costs of all this to Amazon will not be directly related to the carbon cost of the activity (we don’t have a ‘carbon currency’), but it will be fairly closely aligned.
i.e. even if they bought in some smaller boxes, specificly for smaller items, it won’t actually necessarily reduce carbon usage.
so there.