If you rally displayed 1080p on 4K display you would see small image in the middle of the screen with thick black borders all around. Your display is 4K native fixed resolution. If the image is filling entire screen or at least from left to right you have scaled 1080p input signal to 4K. If you see 1080p from Blu-Ray it means that the up-scaling is done in the TV (preferred method). If you see 2160/3840 the up-scaling was done by Zidoo. Typically you would want the signal to be transmitted as close to the source as possible without any scaling, conversions or skipped frames. Let the TV to do up-scaling and signal processing to match best ability of the display panel.