Looking at last seasons NET numbers is pointless, especially in this transfer era. Even Akron, which was much less impacted by the portal than many, is looking at 4 new starters in their lineup. It's very much going to be a different team compared to last season. Many mid-majors are turning over half their roster.
From my understanding the first round teams are matched based off preseason expectations. That would mean expectations are that Old Dominion and JMU are projected to be 2 of the Sun Belts better teams. That doesn't necessarily mean that it will play out that way as preseason predictions are educated guesses. It's the 2nd round that uses NET to determine match-ups.