Greetings.
I tested the app on 5 more devices and the results were perfectly accurate. I have added "Solved" to the thread title.
PROLOGUE
On the HP21, if you take the 13.6 inch approximate size and multiply it by [actual (xdpi or ydpi) / reported scale of 160)], the result, 18.3+ comes closer to the actual size of the screen.
So, if you want to get a more consistent reading, you may apply this factor.
The case for the Dragon Touch is interesting because it reports like a larger tablet, 9.2, but it also behaves like one.
MY CONCLUSION
The issue of developing for multiple screen sizes has been a bit overwhelming when compared to the Windows PC environment. As Google says, "Be together. Not the same." But I am firmly committed to development for Android as it is the dominant OS in the world. Couple that with the power of Google Play Marketing and it is a winning combination. Finally, add B4A to the mix and you have a winning formula.
MY APPRECIATION
Thank you, Erel, for B4A, and for all of your contributions to the forum. Thank you to all participants in the forum who freely give their wisdom and time to enrich this venue.
Sandy