Questions in understanding the transmit power settings and RSSI values

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To evaluate and understand the transmit power settings and resulting RSSI values at the remote receive, I have two ESP12e boards placed side by side within an inch of each other. [I have also tried placing the boards such that their antennas are within an inch of each other.]

On the transmitter I invoke "system_phy_set_max_tpw" using value of 1. The receiver reports RSSI values anywhere near -45. When I increase the transmit power to 82 the receiver reports RSSI of values between -16 and -20.

Questions:
1) Are these numbers reasonable and within expected range? For the ESPs are the RSSI values the received power in dBm, or is it just a relative number? What are the min/max expected?
2) For a fixed max power setting of value 82 to the API, why do the RSSI values vary so much even when the two boards are so close to each other (almost touching)?