Your CINR looks very good. When it gets down below 18 you could notice reduced speeds.
I found this info some years back on the Clear site:
"CINR stands for Carrier to Interference-plus-Noise Ratio (CINR), expressed in decibels (dBs). CINR is a measurement of signal effectiveness. We use the CINR score to tell us the signal strength received by the modem. The higher the number the better signal you are receiving. You need at minimum a CINR of 8 or greater to receive consistent service. A CINR score of 18 or higher is considered excellent signal strength.
RSSI stands for Received signal strength indicator RSSI is a measurement of the power present in a received radio signal. We use RSSI score to tell us if we are receiving interference in the signal. A RSSI score of -100 reflects a lot of interference in your signal, a score of -50 is an excellent RSSI score and reflects little to no interference present."
I would try an easy to make corner box reflector. Experiment for best location of the modem in front of the reflector.
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