Thanks for some extra info. The Estimote apps don’t allow to directly change the power and intervals of the Location packet — they automatically manage these two settings based on whether you have Estimote Monitoring and/or Estimote Indoor Location (the latter is available in Location Beacons only) enabled. This would explain why you’re seeing it reset.
If you do want to manually manage the interval/power of the Location packet, you can make an appropriate “pending settings” in Estimote Cloud, then connect to the beacon in the app, not touch anything else, and disconnect. I think that should do the trick (;
In vast majority of cases, changing the transmit power doesn’t affect accuracy at all. It simply shifts the power curve, so everything becomes weaker or stronger, but the general properties of the Bluetooth signal stay the same. But a lot also depends on the environment, so let us know your findings (: It’s worth noting that this can cut both ways—we once run a test similar to yours in our test lab, and if I remember correctly, in our particular environment, lowering the signal strength decreased accuracy.
(Finally, note that -40 is extremely low power, the range should be like, centimeters to maybe a couple of meters.)