MCS = Modulation Coding Scheme

As MCS increases, Tx dBm is reduced.
As MCS increases, RX sensitivity gets poorer.

https://dl.ubnt.com/datasheets/nanostationm/nsm_ds_web.pdf
https://i.mt.lv/cdn/product_files/LHG_5_all_180105.pdf

I was running my Kettering<>Centerville link at 10 MHz bandwidth.
Was getting MCS12 (max 39 TxMbps @10 MHz) tielding ~ 20 TxMbps.
Tx was likely throttled back 2 dB and receive sensitivity -11 dB

I changed the bandwidth to 20 MHz, got MCS10 (max 39 TxMbps @ 20 MHz),
lost 3dB in bandwidth SNR,  gained 1 dB in Tx dBm, gained 6 dB in receive sensitivity,
bandwidth dB loss, Tx dB gain, Rx dB gain;
               -3,         +1          +6 = 4 dB more SNR.

Simple rule; use the largest bandwidth that yields 15+ dB SNR.

Chuck