Over at the Writers of the Future forums, there seems to be quite a discussion on what kind of stories have had success in the competition. Not only do I mean the genre, such as hard SF vs. yet another vampire story, but the form of the writing, such as first person vs. third person, past tense vs present tense, how many words winning stories have had, titles and structure.
While it appears as though the judges do prefer particular styles of stories and formats, attempting to quantify and create a formula for your writing isn't the way to go.
Yes, some stories are going to suit WOTF more than others will (And don't forget that although it is treated as a competition, it is ultimately a market trying to fill an anthology) but the truth is they do reward well written, well told stories.
You should be writing your stories in the tense and POV that best serves the story. And use as many words as it takes.