Problem defining data rate for lora comunication

Hey all, as I have a mobile end device (tracker), I wanted to disable ADR and define a spreading factor value, but I tried all of the variables since DR_SF7 to 12 and DR_SF7CR to 12 and even DR_NONE and DR_SF8C and it always goes to the spreading factor of 10. Not that this SF doesn’t suit my needs, but I wanted to understand why this happens. I’m using AU-915 to comunicate to my gateway.

To help volunteers would need to know what device, what firmware and most importantly how configured (at device level and on console registration)…

Does it start at that from 1st message or does it move to that after using an alternate SF to begin with, is that from a fixed location or over all uses (in the field)…details will be informative!