Yeah try with bigger pieces, and if you can (i.e. if it's safe), do it indoors - flash paper loses a lot of it's 'flash' property when used outside during the day.
Also, try leaving a sheet of flash paper out somewhere dry for an hour before using it - I'm not sure why, but this seems to help too. Leave it out 'to dry', cut a piece the size of a playing card then fold it in half twice - the results should be significantly better and probably nearer what you were hoping for.
Don't forget, though, that the specs don't know it's flash paper, and don't even know it's fast-burning properties, let alone the brightness and size of flame. If it disappears quicker than they expect, then the flash paper has still surprised them - even if it's not quite how you wanted it too.
I'd recommend you buy Jay Sankey's "In a Flash" and have a go with your flash paper then. You'll learn about how the paper behaves and also you'll have a superb effect under your belt.
I'm a firestarter, twisted firestarter!
Keith Flint from Prodigy lives only 8 miles from me!