Here's a quick sketch to show what I meant in my post:
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I think there's a Black Border (or at least a dark one) hanging down between Goofy's Screen and the Train Window that blocks the top of the screen. Not especially elegant, but better than simply letting the edge of the screen be visible with negative space above. This is the impression I got while riding in person, anyway.
And as mentioned above, Goofy's screen is Transparent, so you can see through all the spaces that aren't showing Goofy to the deeper interior of the train with the bells and whistles. The train backdrop is on a separate plane from Goofy, which makes a big difference over the whole thing just being a flat screen. Gives you a nice parallax between Goofy and the Backdrop, making him feel like a living cartoon in space.
It would have been nicer if that masking had been incorporated a little more into the design of the train - even something like this Photoshopped image below would make it look a little less like an accident. But I don't think they actually left the top edge of the screen totally visible - it never looked that way in person to me.
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