I'm sorry I missed the thread early on. I'd advise against putting the EZ Tag in the trim panel near the dome lights.
While the window is clear and the roof is clear, the spot behind the trim is the tridion cell - full metal reinforcement across the mindshield between the A-pillars.
The metal should be very effective at blocking most of the radio energy; some may get through or bounce around and actually work, but I'd recommend against it - it probably won't work reliably.