[mothered]

Is there any reason why EB doesn’t work on items heavier

If an external Investigation Is opened by the company, they'll cross-check the weight recorded at the carrier's depot.

Heavy Items will register on their weighing facilities, hence the Item's weight will be detected and It could not have been missing.

also is it the weight of the box (eg aipods packaging box) or just the item itself (airpod case and pods)

In terms of the AirPods, It's the Item Itself - "net weight".

If the shipping/gross weight (Item & packaging) of other products Is less than the missing Item method's weight bracket, you can claim the lot was missing.