ADXL372 INSTANT_ON threshold

Hi!

I'm having issues with increasing the instant on threshold on the ADXL372 from low/default (10-15g) to high (30-40g). Im setting the INSTANT_ON_ THRESH bit (5th) in the POWER_CTL register (0x3F), but it doesn't seem to make a difference as it starts spitting out data from equally light impacts (as when its on low). I'm making sure that the correct bit is set by reading directly from the register. I make sure that it's in full bandwidth mode before starting INSTANT_ON mode. Everything else works fine, it's just this but it turned out to be a bit important.

I've tried playing around with filters, filter settle times etc. and combing through the data sheet, but I'm out of ideas at this point, so any insight would be much appreciated. 

NB! I'm on using the ADXL372 on the Nordic Thingy:91 with Nordic Connect SDK/Zephyr, so the issue might result from that, but they have both have been unable to help so far.