I hadn't thought of it, but that's actually a good point: wouldn't the Helios Hotel be too tall and wide to hold regular fireworks shows that are launched from behind the hotel and were intended to be viewed in Cosmic Park?
I can't imagine they would be launching fireworks off a hotel full of people on a regular basis and there is nowhere in the park from which to launch fireworks as far as I know, so I think launching them from behind the hotel is the only option. The logical viewing spot would be the areas around the fountains, but they're right up against the hotel.