Let's look at the PER for each game Mangum and Heaps in relation to the defensive PER average for their freshman opponents. 

Mangum has been better than the opponent's defensive PER in seven of ten games. And the worst he has been is 35.58 points below that number. The best he has been is 172.55 points above that number.

Heaps was better than the opponent's defensive PER in three of 11 games. The worst he was, was 45.38 points below that number. The best he was, was 75.34 points above that number.

If you rank their games from highest to lowest PER, Mangum has three of the four best and six of the ten best. Heaps has seven of the ten worst. 

Heaps was NEVER as good as Mangum as a FR.

The BYU QB's PER will be listed first, then the opponent's defensive PER and the difference

Mangum:

vs Boise St: 162.70 113.18 +49.52

at UCLA: 110.20 111.51 -1.31

at Michigan: 59.36 94.98 -35.58

vs UConn: 128.79 112.14 +16.65

vs East Carolina: 187.24 125.62 +61.62

vs Cincinnati: 139.90 127.82 +12.08

vs Wagner: 321.60 149.05 +172.55

at San Jose St: 132.19 119.31 +12.88

vs Missouri: 114.14 114.29  -.015

vs Fresno St: 150.06 141.15 +8.91

at Utah St: 176.85 123.42 +53.43

Heaps: 

at Florida St: 89.92 119.22 -29.3

vs Nevada: 96.08 119.80 -23.72

at Utah St: 83.05 128.43 -45.38

vs San Diego St: 107.20 113.41 -6.21

vs TCU: 58.81 94.93 -36.12

vs Wyoming: 100.58 138.48 -37.9

vs UNLV: 162.25 161.61 +0.64

at Colorado St: 242.64 167.30 +75.34

vs New Mexico: 137.51 153.17  -15.66

at Utah: 114.74 137.07 -22.33

vs UTEP: 166.61 131.39 +35.22