RPI is the major seeding factor, a lot of other things go into seeding too, but bottom line is that without the RPI to make the NT, you aren't going to the NT without winning the conference tourney. The better you do against a better schedule, the better your seeding will be, if you make the cut. Wins/Losses against Top 25 teams. W/L Vs 1-25, 26-50, 51-75 RPI teams etc. All those things affect both your RPI and your seeding.