Lower Channels have Lower Signal Strength and Transfer Rate
I think arbitrarily wanting to keep the channels 'high' for a mere 3dBm increase is not reasonable.
When I was confronted with this issue (using lower channels for the 5GHz band) I found out to my surprise that the lower channels were superior in throughput.
I don't know if Asus or RMerlin will be able to change this behavior (I doubt it), but you can try doing throughput tests with your current configuration and with using the lower channels too.
I think you may also be surprised (as I was) that the lower channels, although theoretically inferior, perform better in the real world.
I tried an experiment to determine the effect of Channel Choice on Signal Strength and wireless transfer rate.
Experimental Set-Up:
- 2X Asus RT-AC66R routers using Asus-Merlin FW ver. 374.40 Final
- Router locations fixed at 15 meters apart with 3 wall between.
- Routers positioned directly opposite each other in the upright position (on the stand)
- Routers at the same horizontal position (approximately 1.2 meters above the floor).
- Routers connected on separate WAN IP addresses (completely separate networks) to the modem with CAT6 Ethernet cables (this should not matter). These routers cannot communicate to each other by wireless or hardwire connection unless I open a port or VPN tunnel.
- Router "#1" connected by CAT6 cable to Intel 1217 T-1000 Gigabit Ethernet Adapter on a Lenovo Thinkserver TS140 server (SATA III busses) and a Crucial M500 SATA III SSD.
- HP Elitebook 8440p Laptop (SATA II busses) and a Crucial M500 SATA III SSD with Intel 6350 dual band N300 wireless adapter card located 3 meters from Router #1 on same horizontal plane.
- Router #2 5GHz Radio on Channel 149 with Extension Channel 155 (default - cannot be changed). 80MHz channel width. N+AC setting.
- Router #1 Initial Setting - 5GHz Radio on Channel 161 with Extension Channel 155 (Default). 80 MHz channel width. N+AC setting. 5GHz radio power set at 150mw.
- Router #1 Second Setting - 5GHZ Radio on Channel 48 with Extension Channel 42 (Default - cannot be changed). 80MHz channel width. N+AC setting. 5GHz radio power set at 150mw.
- Only one other 5GHz radio detectable on Control Channel 38 with Extension Channel 42 (Default - cannot be changed). Signal Strength varies from 5% at Router #2 location to 0% at Router #1 location.
Experimental Results:
- Router #2 detecting signal strength of Router #1 on Control Channel 161 of 73% power.
- Router #2 detecting signal strength of Router #1 on Control Channel 48 of 53% power.
- Wireless transfer speed of a 3GB .iso media file from the HP Elitebook 8440p to Router #1 on 5GHz Control Channel 161 = 21.3MB/sec
- Wireless transfer speed of a 3GB .iso media file from the HP Elitebook 8440p to Router #1 on 5GHz Control Channel 48 = 21.0MB/sec.
- Wireless transfer speed of a 3GB .iso media file from Router #1 on 5GHz Control Channel 161 to HP Elitebook 8440p = 23.8MB/sec
- Wireless transfer speed of a 3GB .iso media file from Router #1 on 5GHz Control Channel 48 to HP Elitebook 8440p = 18.5MB/sec.
Analysis and Conclusions:
- Changing the Control Channel on the Asus RT-AC66R router from channel 161 to 48 resulted in significant signal strength loss (73% to 53%).
- Changing the Control Channel on the Asus RT-AC66R router from channel 161 to 48 made no change in the uplink speed (from Laptop to Router). Probably because the Laptops WiFi card did not change channels and put out the same power.
- Changing the Control Channel on the Asus RT-AC66R router from channel 161 to 48 did decrease the download (Router to Laptop) transfer rate measurably (from 23.8MB/sec to 18.5MB/sec). Most likely this was due to the decreased power output of the Router radio on channel 48 vs 161 even though the power output setting was not changed from 150mw.