When it comes to something like a marineland I'm of the opinion that media should be arranged in the manner the filter is designed for. The space between the vertical cartridge and the outlet can be packed however you want it but I think the area in front of the cartridge should be left open in order to assure the water flows through the media evenly. Since the only thing you're using that part of the filter for is mechanical filtration, the biowheel should be taking care of biological, it doesn't have to be fully packed to work. In fact it'll work better if its not.
Watch my tank progress from Craigslist salvage to fishy habitat: Aaron's Tank The only things that happen quickly in an aquarium are bad things.