Anyone else having trouble with the size 2 infant mask staying on the "Stem" for the Pari LC Plus neb cup? The size 1 fit nice and snug. The size two falls off constantly. Which seems minor until the screaming, flailing, really really strong 5 month old you're giving TOBI to has just managed to knock the damn thing off for the seventh time and you're only 5 minutes into the 25 minute treatment.! YUP. It's frustrating. We are using the right stem (Or whatever you call the L-shaped piece) for the mask. I just wondered if anyone found a home-made way to make the thing fit correctly.