Need help with scaling UMG to lower resolutions

I’m familiar with the DPI Curve within Project Settings > User Interface.

However, I’m not sure how to test scaling for obscure resolutions on devices I don’t own.

My game was designed at 720x1280(portrait) and long as the resolution ratio for devices is 16:9 this scaling seems to work fine. EG: Moto X 2nd Gen looks good, Samsung Galaxy S2 does not.

But on some older devices or larger tablets that use 16:10 the scaling is too large. I’ve read I must set points for each specific device but I do not know how to determine what to set them at or how to test without those devices.

A user with a Samsung Galaxy S5 Mini is finding that the resolution is applying incorrectly on their device as well.

S5 Mini specs: Samsung Galaxy S5 mini specs

The game shows properly on an LG G2, LG G3, Moto X 2014, and Moto E 2014. The UMG is a custom size of 720x1280.

I’m not quite sure what could be going wrong, and why some devices see the image below with top and sides cut off (taken from S5 Mini)

Another question: do you have to set the User Interface DPI curve or is it supposed to work automatically?