The logic behind this dynamic resolution is easy to explain too. Inevitably, looking up to the sky in the same initial area - even slightly - to force the demanding elements of this scene out of view, the Snowdrop engine switches itself to a full 1080p. But as you'd expect, lowering the camera again (bringing all objects and fog effects into view) gets us back to 1792x1008.
http://www.eurogamer.net/articles/digit ... resolution 