@AndreMartins 

I believe you meant to say that Channel number 165 does not allow you to use 40 or 80MHz wide frequency band. This channel only support 20MHz as per North American specifications. If you do have 4 APs in your environment, I will recommend that you set all APs to use 20MHz chnanel and then test. 20MHz channel might give you same or more throughput that you are getting now with each AP trying to use the same 80MHz wide channel.

Tplink APs being lower cost, do not have the function of continuous scaning to adjust the channels based on interference in the environment. These APs only scan and chose channels at the boot time once. Either you will need to set each AP manually for its channel or you ensure that you dont reboot all 4 APs at the same time. One option is to schedule to reboot the 4 APs every week but at say 15 minutes aprt from each other. Then only one AP will be scanning and should pick up the best channel it can and then after few minutes second AP will do the same and like wise.

Hope this helps resolve and improve the performance of your wi-fi network.

@dpsguard 

I was referring to channel 155 in fact. I still don't understand why some frequencies are not available.

As per the channel width, an wider channel wouldn't give me more performance ? At this moment it is set to use all 3 (20,40 and 80)

@AndreMartins 

Channel 155 only means that it is a 80MHz wide channel comprising of 149 to 161.

https://en.wikipedia.org/wiki/List_of_WLAN_channels

Availability of frequencies depends upon the country you live in.

80 or 160MHz channels are only recommended for home environments where you will only have one AP. In typical small or mid size office, you might be okay to use 40MHz chnanels. In larger setups, requiring many APs for coverage and density of users / devices, it is recomemnded to use 20MHz. The 20MHz chnanel can still provide me easily 100Mbps when tested thru speedtest.net 30 feet away in my own home on my phone or tablet.

So if you will use channel 155, then really you will only have upper channels agregated into one and then you do the same in the lower band ( 36 to 48 channels).

For multiple APs, this will cause overlap of frequnencies and you will probably not see much improvement in throughput. You might be better off using 40MHz channels.

For North America, Tplnk only supports 4 lower band 20MHz channels and 5 upper band 20MHz channels, or 2 lower band 40MHz channels and 2 upper band channels.

If you are in Europe, then you also have DFS channels as mid band that you can use if you dont see much interference from aircraft or weather doppler radars in yoru areas, else as soon as weather radar sweeps, your DFS channel AP will drop those channels as per law and will start looking for the new channels. Accordingly, DFS channels can never be staticaly set and AP needs to be set to auto channel to make use of these.

Hope this helps.