Theories abound about why a No. 12 seed always seems to upset a No. 5 seed. Is it because 12-seeds are typically underrated mid-majors? Or because 5-seeds often don't get to play close to home like top-four seeds do?

One thing not in dispute: No. 12s are the most profitable seed in the first round.

No. 12 seeds are 12-3-1 (80 percent) against the spread the past four years, 24-11-1 (68.6 percent) over the last nine years. That includes an 18-18 straight-up record.

The "12s" went 3-1 ATS in 2017 for the second straight year with Middle Tennessee State the lone outright winner, over fifth-seeded Minnesota.

SportsLine's advanced computer model knew MTSU was the 12-seed to get behind in its bracket. In the past two years, the model has called 12-of-15 first-round upsets, including the Blue Raiders, including nine by double-digit seeds.

This year, the 12-seeds are Davidson (+6 vs. Kentucky), South Dakota State (+8 vs. Ohio State), Murray State (+10.5 vs. West Virginia) and New Mexico State (+5 vs. Clemson).

Based on the spreads, oddsmakers give New Mexico State the best chance to advance. But the model is going big on a different No. 12 seed.

Will Davidson make a Cinderella run like it did a decade ago with Stephen Curry? Will South Dakota State extend its 28-win season? Will Murray State, the Ohio Valley conference champ, give Bob Huggins another early exit? Visit SportsLine to see the optimized NCAA Tournament bracket, and see which underdogs to lock in now, all from the model that nailed nine of 12 upsets by double-digit seeds the last two years.