MPU60x0 digital low pass filter characteristic?

Hello!

I´m looking for the DLPF characteristic. I use the setting DLPF_CFG=3 (Accel=44Hz, Gyro=42Hz) and performed a shaker calibration for the acceleration sensors.
There I got the following signal attenuation:
1.5% at 12Hz,
3.6% at 16Hz,
6.3% at 20Hz,
10% at 25Hz,
16% at 31Hz and
22% at 40Hz.

This I find very high attenuation for frequencies below 44Hz.

Where is the cutoff frequency? What is the filter characteristic? Is the filter frequency sampling-rate-dependent (it is set to 128Hz)?

Thanks!