Issue with the simulator and template:
The drawing space for the Top screen is still 400x240, but the top screen starts loading the image 6px to the right for some reason. The additional 6px space to the right is also unnecessary.
Take for instance the theme attached to this post: Invisible space is denoted with pink, green and red, and the margins are denoted with 3px-thick deep blue borders.
When loaded into the console, the green, red and pink spaces are invisible, and the blue borders are indeed there and they're 3px thick:
The theme simulator and the template need to be updated to reflect this.
For the record, this happens with official themes as well.