I received a sample large meluna when I ordered the medium. I tried out the large one yesterday and it was really uncomfortable - I couldn't insert it deeply enough so the bottom of the cup pushed down on the opening of my vagina and I had to concede it wasn't going to work out.
I've looked at the comparison chart here http://menstrualcupinfo.wordpress.com/cup-stiffness-comparison-chart/ and see that the small fleurcup has the same body length as the medium meluna but has a higher capacity. With the 15ml med meluna lasting 5 hours on a heavy day I worked out mathematically that the 22.5ml fleurcup should give me 7.5 hours.
I'd really love to hear from anyone that has both a medium meluna and small fleurcup as to whether they both feel about the same to wear and whether they feel the capacity of the fleurcup does give them a couple of hours extra before emptying.