This is a difficult question to word in one sentence, so there may be an answer here, but I haven't found it.
The issue I'm having is displaying my web app on different devices. Specifically when projected at meetings, for example. On my computer and on server, I set the full extent to cover a certain area (the conterminous U.S.). I also set the caches to use the same scales as ArcOnline's preset scales for zooming in and out.
On my computer and other computers it works perfectly, but when I plug in a projector the scale tends to be quite different. Using the U.S. example. instead of showing all 48 lower states, it cuts off S. Florida, and all the states like Washington to Maine. When I "zoom out" by one set amount, it not only covers all 48 lower states, but much of Mexico and Canada and the oceans.
Why does the scale change like that? Does it just have to do with the aspect ratio of the computer screen vs other screens?
If that is the issue, is there a way to "reword" the scales so its not set in stone like 1:50,000 but based on lat/long or something like that?
My guess is the "why" has to do with screen size and resolution. Setting it toa scale factor has to still deal with the physical hardware available.
It will also have to default to one of the scale factors that are in the cache. Therefore, if you say zoome to the lower48 and it's a small screen, you mage get one of the lower scale caches (for my location, that is 1:16m), but if you have a large scale or a higher resolution, it will choose a scale factor with finer detail.
I do now know if there is a way to override this behavior on AGOL...but you may be able to do something if you have a custom app with Web Appbuilder developer edition.