Oooh, we all have slightly different methods it seems! I always make it using 200 mls very cold water from the fridge : about 3/4 (thats three-quarters, not 3 to 4 scoops!) of the scoop shaken into the mousse mix in the packet and stirred really well.
As soon as I add the dry mix to the water I whizz it with an electric hand blender for about a minute, then pour mixture into a sundae dish and pop back in the fridge for about 5-6 minutes. It's light and fluffy with an Angel Delight sort of texture.
Enjoy experimenting !! xx