RBOmniTikU-5HnD channel width frequently switching 20-40 mhz

RouterOS Wireless Networking
1

I m using Ominitik(RBOmniTikU-5HnD) as AP and ligodlb 520n as a station
my problem is AP frequently switch between 20mhz and 40 mhz when this happen my throughput will decrease dramatically
I m giving 75mbps speed to my customers which is easily got my customers when AP work on 40 mhz but when AP randomly switch to 20 MHz my speed reduced to 30 to 45 mbps
I can resolve this to set ap channel width to 40mhz only but there is no such option, there is option 5mhz, 10mhz, 20mhz, 20/40-eC, 20/40-Ce, 20/40-xx
there is no option for 40mhz only, I only want to use 40mhz
I already tried these tree option (20/40-eC, 20/40-Ce, 20/40-xx) but my problem is same
I m also using some other vendor AP (nanostation m5) they provide 40mhz only option when I set to 40mhz only this is never switch to 20 mhz

I really appreciate mikrotik if they can add 40 mhz only option in channel width

thanks

2

Reduce the number of data rates advertised by your AP.

example
basic-rates-a/g=36Mbps,48Mbps,54Mbps
supported-rates-a/g=36Mbps,48Mbps,54Mbps

3

yes I tried this but problem is same
I want to enforce 40 MHz bandwidth for continuous higher bandwidth