My only real 'rail shooter' experience that I can recall is the original Star Fox on SNES, but I remember that in that game the 'zone' for movement was large enough that you could slightly pull the screen in the direction you were going to give the player more space (I would say roughly a quarter of an extra screen's worth) while flying through the main level and only focusing back down to a single screen's worth of movement when it became time to fight the stage boss. Adjusting the levels to take this into consideration obviously means more work, but it would also mean that the player has more breathing room to work with and gets a better feeling that they're actually flying, and allows for more varied placement of enemies, items, and secrets.