I used to have water leaking into that exact area.
Having blown out the drains and checked the tubes many times without fixing the problem, it finally dawned on me.
The seal around the sunroof panel is actually slightly higher on the outside of the removable roof than on the inside.
If the seal is not tightly fitted to the removable roof, water can collect in the channel of the seal and actually make it's way into the car interior and past the drain.
Here is a crude picture of what I'm talking about.
The low point around the seal is just over the floor in the back seat area. This was the only wet area in my car when it leaked.
My solution was to put a bit of silicone sealant onto the sunroof seal to attach it to the remavable roof panel with a water tight bond.
No more leak!
I've been leak free for at least 10 years now, and haven't had to unclog the drains once.
If your drains check out OK, check to see if the sunroof seal fits tightly.
Jamie