Interesting. So they can fit close enough to hold it in place then. I knitted a spare ribs shoaker but my son was 18 months or so at the time and so to be honest he was not a fan of the idea. I didn't really get a chance to try it out properly. Oh I have loads of prefolds. My mum got me 2 of the small 12 packs, and I got a lod more of the size 2 and some more size 1's 2nd hand. We haven't used them really for daytime use since DS was 12 months (in the house he had underpants and a microfibre cloth) so I'll haev to get used to a full nappy load again. Now we're only on nighttime nappys and then the odd one used for daytime juice spills!
I'm guessing a wool soaker with ribbed cuffs would be best for containability. Now I do actually have a fair stash of wool so that is something in theory I could do, that is after I finish the wedding present for May, and then do a baby blanket and the bunting (which I really want to do as it looks cute and is half finished as it would've been for my sister, but not entirely sure how necessary that will be for an august baby).