ADXL372 external clock with instant on mode

I am trying to use the ADXL372 in instant on mode with external clock. 

1. External clock on INT1 at 614kHz and INT2 mapped to AWAKE. In this case the INT2 is not raised when there is impact. But INT2 is raised without any impact time to time. 

2. INT1 mapped AWAKE and instant on mode is set. When AWAKE interrupt occurs, INT1 is used for external clock from the microcontroller. Once the data is read from the ADCL372, the INT1 is mapped back to AWAKE and external clock is disabled. This configuration works most of the times but misses the impact detection sometimes.

Question is, is the configuration of external clock with instant on mode possible? if so, please let me know specific steps to enable this configuration. And, please confirm  which of the above configurations are better for the external clock usage.