Sponge-bio-sponge is my best suggestion... if you wish to add Carbon to that I would put it in the middle of the 'sandwhich' with the bio...
Having the sponge on top of the AC filters minimizes bypass & greatly reduces the liklihood of the media 'floating' which can result in several undesirable results...
But as mentioned, mechanical filtration (sponge) needs to come before chemical (carbon) or bio filtration. Either of these medias (bio & carbon) will be less effective if physical waste is allowed to collect in them...
Based on this conversation, it sonds like you (Nick) understand that, but I just like to explain for clarity to others who may be following along.