Assumption: You have this option set in the ePO config: "System Tree sorting: Sort systems on each agent-server communication"
What I would do would be to create a TAG where the criteria is an IP on the "warehouse" subnet. Ensure that this option is checked "" in the evaluation tab of the tag create/edit menu.
Then add the tag to the warehouse system tree branch as sorting criteria. Then I would place that system tree branch at the top of the sorting order.
Hopefully, this will be more consistent in sorting for you.