That's how they try to do it, but sometimes, it's not possible logistically, for whatever reason.
The only hard and fast rule is that the top 2 seed (#5 overall) can not be in the same region as the overall #1.
That will be especially difficult this year as I'm sure they will try not to have SEC teams at 1&4 or 2&3 in the same side of a regional bracket. They may have to once but it probably isn't preferred.