Sample rate of DMP

Hello,
I am having some problems configuring the sample rate of the DMP using the Embedded MotionApps source code.
As far as I understand it I can configure the sample rate by modifying the function parameters of inv_dl_cfg_sampling which is called by umplStartMPU.
I have tried it this way and it works up to 380Hz. If I try to go higher with the sample rate (e.g., inv_dl_cfg_sampling(7,19) which should result in a sample rate of 400Hz) the MPU appears to be running with a wrong sample rate (for the former example it appears that the DMP is running with a lower frequency).
I test the actual sample rate by measuring how often I get interrupts on the interrupt pin which should shows interrupts at (sample_rate/fifo_rate_divider).

Can You explain to me what I am doing wrong?