In general, I have noticed that web applications built using ArcGIS Online and WAB Developer Edition both have the following problem. If you set the initial extent of the app on one machine, the app may be zoomed in or out one level of detail on another machine. I've seen this so many times and I believe it is due to differing aspect ratios of the monitors. My monitor has a 4:3 aspect ratio, so I'm the odd man out.
Intuitively, the app zoom level should be the largest LOD that completely displays the initial extent. If the map does not contain the initial extent, then something is wrong. If it is zoomed out unnecessarily far, then something is wrong.
This seems like it should be a well-known issue. Could anyone please explain it at a detailed technical level? I think it may have to do with the fixed LODs of WAB.