-
Correct - I've got Ortlieb City panniers and the front are 12L and the rears are 20L. The crossbar with the mounting equipment is less than 2/3 the width on the front than the rears.
I've had no problem putting them on a Pelago Rasket rack (also seen people running Restrap panniers on there too).
I even managed to find a picture!
https://flickr.com/photos/31039403@N08/48575945881/in/album-72157710418558712/
You're welcome.. I think most rear panniers are twice the size of front panniers. The Orliebs we have are around 12 liters per side and the Carradice 10 liters per side.