Smart Connect is just not smart enough. Upon more investigation, I have indeed seen it use Channels 6 and 11 in addition to Channel 1.
Today it decided to use Channel 11, and I could not get a proper connection, even though there was plenty of signal. The problem was that my Chromecast is also on Channel 11, and it was the same strength as the signal from the DIR-890L. When I walked into the router room, it connected.
There seems to be a fundamental problem with the algorithm used: The router only sees the signals at the router location, which is not the same as the signals at the devices.
Will the 890L connect on channels other than 1, 6, and 11, which are all busy with neighbors traffic?