Lunette size 2 not sealing?

My period started off rather heavily this month and my small Keeper Mooncup filled up too quickly, so I decided to try out a size 2 Lunette. And somehow, as much as I doubted it would ever be this way, it seems to be the cup for me. The capacity is much better suited to my flow and it is so much easier to remove because of the ridges on the stem and the base of the cup (and the stem doesn't bother me at all like my Keeper's stem does, which is annoying because I don't think I could remove the Keeper without it).

The only problem is that although the cup opens up without any problems, I don't think that it's really forming a good seal. I could never rotate my Keeper at all but I can turn the Lunette continuously and it doesn't seem to make any difference. This has resulted in some leakage, albeit very slight, as I think the cup leans to one side or slips a bit too far back.
 
Anyone have any tips as to what I can do?