sfx2000
Part of the Furniture
In my neighborhood, there are inconsiderate folks who force 40 MHz.
I would not worry too much about that - the secondary channel is opportunistic at best, and looking at a spectrum analyzer, most of the traffic is on the Primary/Control channel...
In 802.11n, it's actually impossible to force all traffic over 40Mhz for 2.4GHz, no matter what the AP setting is.
Always better to just plan for 20MHz channels in 2.4...