What determines the location of a Grease P. stroke depth wise? (same layer)

Now I know it is not their order in the collection.
Also each stroke is located in the same place (X,Y,Z).
So then, what is it?

Thanks guys

I found the reason: The time when the stroke is created determines how it will overlap with respect to the rest. However, they will still maintain the same location in space, somehow.
Hence, if you can plan ahead your workflow, then you can arrange them accordingly. If not, then you can always push/pull them on the depth coordinate as needed. For example, if I am on the Front view, then the Y will be the coordinate for depth.