Depending on what else is in the suitcase, dirty washing etc. can shift about.

My fizz comes from a very good small supplier who brings our orders down from Champagne twice a year, so I'm regularly transporting half a dozen or so. I would recommend packing the 'poo into a proper (6-bottle) wine carton, as solidly as possible, and then packing that, with some foam/bubble wrap, in a (large-ish) hard-sided suitcase. This has never let me down, including to CBR via CDG, HKG & SYD. (I've also shipped 12-bottle cases without problems as out-of-gauge but BA in Y now limits you to a single item. LX is OK, as I get 40Kg with my LX/LH Silver.)

(Anyone in the GVA area wanting supplier/delivery details, please PM. Collect from French side of the border only.)