How to attach Units to Spawn Reposition Module?

[Trinket 5]

I want to attach my units with dark blue lines to a respawn position module (f5), however I cannot get get it to work.

 

To give you an example of what I mean:

Here you can see the units are grouped and attached to one unit leader (light blue lines), but are also attached to the respawn position module (dark blue lines). If I add more units, which I need to do, I cannot add them to the respawn position module. I have tried holding CTRL whilst trying to drag a line between a unit to the respawn module, like I would to attatch them to a squad leader, but nothing. I have also tried holding ALT and doing the same, moving them ontop, etc, nothing.

 

Can someone please tell me how I can attach new units to the respawn position module?

 

Thank You.