Well, MCS9 is a very very bad idea. This coding scheme offers zero protection, and it requires a C/I above 30dB and a RXLEV DL > 85dBm in order to provide acceptable throughput.
I strongly recommend you move back to MCS-6, or even MCS-5. Beware, MCS3 & MCS4 are not resistant at all.
FYI, this is the list of coding scheme from most resistant to less resistant :
this is approximate.