I'm sorry to bump such an old topic, but I'm having a similar issue.
I have the Steam version of Eufloria; I originally bought it on a computer with a massive 2560x1600 res monitor-- loved the LCD, a bit too big for my eyes though. I downgraded to a smaller monitor that's 1650x1080, then my desktop exploded and I had to replace it. I copied the files from the Steam directory and reinstalled it, but the problem is that fullscreen is still stuck in 2560x1600 no matter what, even on a new computer.
I've tried deleting all the Steam files and redownloading the game, and it still keeps fullscreen stuck at the massive res. I've searched my computer for all references to Eufloria and Dyson and deleted them, then redownloaded and reinstalled the game, and I still can't get fullscreen to scale to anything lower.
Is there any manual way or configuration file I can edit to stop it from doing this? It's really driving me crazy.