Hi,
If you have a Windows laptop, get a copy of INSSIDER, install and run it. It will give you a wealth of information regarding your router and all of your neighbors signals too.
If you have an android device, use the WIFI ANALYSER app, it gives you a graphical representation of signal strength, channel congestion, and it is easy to use. Their is a little tab towards the left top where you can change between 2.4GHz band and the 5 GHz band.
I have found no difference in the rotation of the DIR-868L has any impact on speed or coverage. Placement is usually best away from electrical equipment and metal ductwork and a central location in your home is recommended. I have mine in one corner of a 1700 sq. ft. ranch home and I get good coverage everywhere on both bands.
Good luck
As a side note, I think the SmartBeam stuff actually works, as before I connect a device, it might indicate 3 bands, but as soon as I connect, I get 5 bands.