OK. Checked it and currently I can only provide two solutions.
Enable Black borders. It don't fix that margins but looks better.
Use Stretch not Upscale. It will remove margins but obviously impact quality as image ratio will be little distorted. I tested it on Keyboard model - decrease of quality is not so high.
I will think about adding some code that will allow panel view to skip margins but it is not a simple matter and don't expect that soon.