Let's break it down further. I'm going to use the Massey composite rankings since they are much better than the AP, and the end of season rankings since they are more indicative of how good a team was than the current week rank (which can be hugely inaccurate earlier in the season).
Against the top 40, Bo is 16-22 with an average score of Nebraska 25, Opponent 30. Here's a breakdown of that:
vs. 31-40
Record: 6-1
Avg. Score: Nebraska 32, Opponent 17
vs. 21-30
Record: 5-4
Avg. Score: Nebraska 25, Opponent 33
vs. 11-20
Record: 4-8
Avg. Score: Nebraska 20, Opponent 29
vs. 1-10
Record: 1-9
Avg. Score: Nebraska 27, Opponent 37