How to determine which selected object is on the top from multiple AIS_InteractiveContext when clicking to select objects in V3

How to determine which selected object is on the top from multiple AIS_InteractiveContext when clicking to select objects in V3d_Viewer?
I am currently iterating through all AIS_InteractiveContexts, calling SelectPoint to find the topmost object in each context. However, I cannot determine which object is truly on top among those selected across multiple contexts. Due to requirements, I cannot use a single AIS_InteractiveContext. Thank you for your guidance!