That's an important point!
Moon/Sun Roofs do not seal. They divert the water coming around the roof into the supporting pan.
Then there are 4 drains to put the water on the ground.
So check your drains and realize if you get in enough rain you will get some leaks. It's just the design of the unit.
Even my 2005 Jaguar Moonroof operates exactly the same way. Kind of confusing when you first look at it.