This message was posted on behalf of Intel Corporation
Thanks for reaching out!
According to https://forum.arduino.cc/index.php?topic=377620.0, the RSSI value is available internally but not exposed as an API. So, it seems that this value is not reachable from an Arduino sketch. However, this post is old, so, there may be news. Since this question is directly related to Arduino sketches, then you might interested posting your question in the Arduino community (https://forum.arduino.cc/index.php?board=103.0), they may be able to provide you a more accurate response.
Also, since you are using TinyTILE, you might also want to try asking in its forum (https://www.element14.com/community/docs/DOC-82913/l/tinytile-intel-curie-module-based-board), perhaps they can also be of help.
I hope this information helps you,