Initializing ACCEL and GYRO for DMP

Hi, to try to ensure I understand this process well enough to use it for our hardware needs, I am porting the 6 axis motion tracker DMP to python (from the 5.1 SDK). It all works great, except for two things. When I try to initialize the GYRO for the DMP (DMP memory 976 plus 12 bytes in the motion tracker DMP), the scaling of the bias is off. That I can fix. And write to DMP memory. So we have the 3 axis QUAT working great. But...

When I do the same with the ACCEL, I note that the ACCEL readings taken from the subroutine get_st_biases are DIFFERENT from those placed in the FIFO while the DMP is running (the chip is physically immobilized). They are not just different in scale - but there are offsets, and this of course impacts function.

I came across the use of the 0x03-0x05 and 0x06-0x0b registers for acceleration bias in the inv_gyro.c code that is not used in the motion tracker library. I was wondering if these biases are used to compute the ACCEL in get_st_biases but not by the DMP (or vice versa)?

More simply, why are the ACCEL readings taken from the FIFO in get_st_biases not scaled-identical to the readings taken while the DMP is running?