Theoretically what you say above could happen. Although with all the promotions we have run using this format we have yet to see anything even close to a 1000%. Most 1st place finishers generally come in around 130% range.
That is why there is minimum betting requirements of 150 rounds and 0.05 BTC wagered. So a player can not play just 1 round and have a sky high winning percentage.
Actually your requirements is not so effective, whales who are interested with the prize can easily win this because they can just made 1 bet with a bit higher multiplier (lets say bet 0.05 with 3x multipler). If they win it = 200% winning percentage (if my math is not that bad), then will only need to make the other 149 bets with the minimum bet amount. I'm sure whales wont be afraid to risk 0.05btc for 1.2btc
If the math is right then that would be the best way to win this tournament. It would be much better in the end to not join and just wait for the leaderboard in the last 3 days. If it is worth it to consider this strategy then Im sure someone would use it to win. Smart people is going to win this tournament not the lucky guy unfortunately