Unless you tell it to use a custom bootstrap class, the Feathers SDK will initialize ScreenDensityScaleFactorManager automatically.
One thing that catches my eye is that 400 DPI is exactly halfway between 320 DPI and 480 DPI, which are the anchors for the 2x and 3x scale factors in ScreenDensityScaleFactorManager. ScreenDensityScaleFactorManager tries to figure out which of these anchors the current device's DPI is closest to as part of choosing an appropriate scale factor. Since 400 DPI is equally close to 320 DPI and 480 DPI, neither one is considered the better choice. Since everything seems small, it sounds like ScreenDensityScaleFactorManager prefers the larger scale factor in this edge case, so it's likely choosing a scale factor of 3 instead of 2 for this device.
What kind of device is it? ScreenDensityScaleFactorManager is based on the scaling behavior of native Android apps. If I can determine that native Android apps use a different scale on this particular device, I will consider tweaking the behavior of ScreenDensityScaleFactorManager to prefer the smaller scale factor instead.