At the moment, ShipStation does not have any way to specify where inventory is pulled from on an item that has multiple locations when allocating orders that have products which use multiple locations. Instead, the product's allocation is automatically pulled from the top of the alphanumeric list.
This can be worked around if the User does not use all 4 parts of ShipStation's Inventory Location by alphabetizing the Area in order of how you want things pulled, but this is not ideal as it doesn't help Users who use all 4 parts of ShipStation Inventory Locations and can also appear confusing to pickers.
This old post indicates interest in this ability as well (though the post is primarily about something ShipStation has since changed). https://community.shipstation.com/t5/Printing-Documents/Pick-list-to-get-product-location-from-inven...
Yes! I am having this issue, and would love the dev team to find a better solution than the current workaround.
For instance if you want to allocate orders from Shelf 3 first, then Shelf 2 next, and Shelf 1 last, you have to do the workaround mentioned above...it would be great if we could choose the order in which inventory is pulled!