The size of the configurator window is 960 x 768 pixel by default. Changing the configurator scale factor to 2.0 (200%) resizes the window to 1920 x 1536 pixel (this is more than your native TV resolution (1440p) can handle anyways).
The problem is probably that your TV upscales the video signal, because your Gfx-Card / Grim Dawn screen resolution is set to 3840 x 2160.
The upscaling could lead to a smaller GI Configurator window and probably to a somehow blurry (lower) picture quality.
But I’m not a TV expert, so my assumption could be wrong!
Anyway, I’ll set the maximum value for the Configurator scale factor to 3.0 in the next patch.