Folding Bikes - Ortlieb Panniers for Birdy - which ones work?

I'm looking to buy Ortlieb panniers for my Birdy. It has an expedition rack. The local dealers don't carry Ortlieb so I'll have to order it over the web and cannot really try out the different sizes. Any experiences? I know the small front rollers work for both front and rear, but what about the sport packer or the bike packer?
I would like to have larger size panniers because I'm planning to do some extended tours.


Thank you for your help!

I have a normal size rear Ortlieb Roller that I can fit on the back rack of my Raleigh when I need it. The biggest consideration is how far back on the rack you can fix it safely as if you fit it centrally your heel will catch it once per revolution of the pedals. I'm sure this would the same for you on your Birdy, as it goes with the territory on smaller wheeled bikes, so maybe getting smaller than standard bags is the way ahead to ensure safe and well secured luggage.

I have the bike packer plus that I use for commuting. I was worried they'd be too big, but they aren't. I can fit a lot of stuff, but they don't seem huge. I have size 12.5 feet and a bike with relatively short chainstays (a Surly Crosscheck). I was worried about heel clearance. Wayne at The Touring Store (fantastic service) hooked me up with a Tubus Cargo rack with a couple little adaptors that moves the rack up and back a bit. The Ortliebs are easily adjustable in terms of where the bags fit on the mounting rails (you can move the top clips around to get more clearance--though I haven't needed to.) That said, with the extra bit of clearance the rack adaptors gave me I have no problems with heel strike and could even move them back a good bit further if needed. I love the combination and think it is better to have more room that you don't need than too little room with everything crammed in.