Update. Aqua-One replied to my question and said the following:
Thanks for reaching out. The Nautilus 1400 water flows into the canister and down to the bottom, then up through the media, where it then leaves the canister from the top of the filter. The easiest way to check the flow of the filter is to check the way the media is set-up, with the water always going through the coarsest first, through to the finest.
I do hope this helps
Kind Regards
Team Aqua One