When multiple copies of an item are assigned to the same library branch, the location drawer appears to list them in order of item record ID within the same location (this is also the case in our classic Polaris PAC, not sure how it is in Sierra). We have had feedback from front-line staff that they would like to see copies in Available status listed first, with copies in other statuses listed below. This reasoning makes a lot of sense to me. If a patron is opening the location drawer, it's because they want to know where the item is on the shelf so they can go and collect it (if they wanted to place a hold, they would be using "Get it" instead). Thus, they will only be interested in the call numbers/shelf locations of available copies, so those copies should be listed first, rather than requiring the patron to scroll past unavailable copies, which is the current setup. This is most noticeable for popular children's titles where it's common for a location to have a dozen more more copies of the same title in the same format.