9 inches by 9 inches at a 200 dpi resolution is the optimal settings configuration for submissions.

What format(s) are best used for submission of contest entries?

jpg/jpg-2000 are the preferred formats for submission and display upon the Inked Magazine website.

When a submission is uploaded at the preferred high quality resolution(s), why when it is viewed does it only display at a maximum of 900 pixels for its dominant dimension?

Submissions are stored at three sizes. The original in its uploaded state, ensuring pristine quality at the time of upload to the Inked Magazine site. A web friendly version which sacrifices some of the print clarity and file size for easier viewing for our lower bandwidth Inked Network members, and finally, a thumbnail sized image for display upon the tshirt backdrop as an indicator as to what the submission might look like upon an actual shirt.