George,
In my main WAB app I add LODs down to the resolution of my organizations aerial photography basemap which goes to 564.2485881 and using Local Layer widget I set the display levels 10,11,12,13,14,15. Normally the Street map base map goes from 1 to 19, I don't use 1-10, and then turn it off at 15 and let my orgs basemap take over (seems how my aerial basemap as a minScale and MaxScale set on the service itself). This just FYI, in case the is helps some. BTW I don't attend the UC anymore I have been going to the Dev Summit for the last 8 years instead of the UC.