When I did my tulle skirt, I did all my layers the same length and it still makes the skirt appear full but for extra fullness, I would probably do the opposite of what you suggest, making the shorter layer on the inside and it gets longer as you go out. But, that’s just me thinking out loud because I don’t know if I’ve ever come across a layered tulle skirt in person. I think it might look a little weird if the top layer of the skirt was shorter than the layers underneath, but you can always do a tiny version of the skirt and maybe the results will be awesome.