It's gotta be the open dome and being a few inches away, why not get a smaller enclosed one that you can place directly on the screen. I've got the same wattage running in my large open iguana cage over a perch and it heats the whole enclosure a few degrees plus makes a 90f hot spot with 80 ambient below it. I also don't see how switching from a glass aquarium to a glass enclosure is going to help your situation any, why not get a pvc cage with a radiant heat panel?