ADXL372 Samples before and after trigger

I am having problems setting the number of samples to be captured after and before event in triggered fifo mode.

For example if I put adxl372_Configure_FIFO(&adxl372, 300, TRIGGERED, X_FIFO); I get a total of 300 samples after the trigger and not 212 before and 300 after as it should be the case according to the datasheet. (For example if the FIFO_SAMPLE is set to 12, there are 500 samples before the trigger and 12 after the trigger.)

code: 

adxl372_Set_Op_mode(&adxl372, STAND_BY);
adxl372_Set_Autosleep(&adxl372, false);
adxl372_Set_BandWidth(&adxl372, BW_3200Hz);
adxl372_Set_ODR(&adxl372, ODR_6400Hz);
adxl372_Set_WakeUp_Rate(&adxl372, WUR_52ms);
adxl372_Set_Act_Proc_Mode(&adxl372, LOOPED);
adxl372_Set_InstaOn_Thresh(&adxl372, ADXL_INSTAON_HIGH_THRESH); 
adxl372_Disable_Hpf(&adxl372, true);
adxl372_Disable_Lpf(&adxl372, true);
adxl372_Configure_FIFO(&adxl372, 300, TRIGGERED, X_FIFO);
/* Set activity/inactivity threshold */
//adxl372_Set_Activity_Threshold(&adxl372, ACT_VALUE, true, true);
//adxl372_Set_Inactivity_Threshold(&adxl372, INACT_VALUE, true, true);
/* Set activity/inactivity time settings */
//adxl372_Set_Activity_Time(&adxl372, ACT_TIMER);
//adxl372_Set_Inactivity_Time(&adxl372, INACT_TIMER);
adxl_write_reg(&adxl372,0x33,0xE3); //0.7g activity treshold int2 pinu
adxl_write_reg(&adxl372,0x3C,0x20); //motion warning int2
/* Set instant-on interrupts and activity interrupts */
adxl372_Set_Interrupts(&adxl372);
/* Set filter settle time */
adxl372_Set_Filter_Settle(&adxl372, FILTER_SETTLE_16);
adxl372_Set_Op_mode(&adxl372, INSTANT_ON);

 Can somebody tell me what could go wrong with this?