You can use a VI Server to position the front panel of your subVI. Look at the Ghost in the Machine.vi example that ships with LabView.
To see where to position the subVI, you need to know the position of the calling VI or of something on it. You could use a property node of the Get Details button.
1. On the front panel on Panel.vi, right-click on Get Details and select Create >> Property Node
2. Right-click on the Property Node and select Properties >> Position >> Left.
3. Point to the bottom edge of the property node and pull it down to add another element. That element should default to Top.
That will give you the coordinates of the Get Details button. Now use a VI server (based on Ghost in the Machine.vi) to place the subVI front panel the desired distance
from the Get Details button.