it is a combination of several factors.
1. Stability- Even though the DC has changed, the philosophy/ideology of the defense has not. If you are not shaking up the ant farm every season, it's easier to adapt.
2. Manning Factor- They are practicing against a high end QB that doesn't give them a break or pull up in practice. You have to be sharp there or it's rock alexander time.
3. Pressure- While the sacks haven't come in bunches, QB's are forced to either rush their reads or throw under pressure.