The Wii2HDMI Analog (Composite/Component) to Digital (HDMI) converter only properly takes in 480i/p resolution dimensions... and upscales them to 720p or 1080p resolutions.
You'll be wasting your money if you try using this dongle to get a Full RGB range, when the picture will still look blurry when outputting at 480p while it's upscaled to a higher resolution.
If you try to set the setting to 720p and pass it through the converter, the converter will only provide with a 'part' of the screen. The converter doesn't actually auto-detect the full picture signal, it just pretends all signals going through it are under the 480p resolution size & upscales it from there... hence only cropping a part of the signal that's bigger than 480p.
Also, tweaking the 'screen size' option won't help... because it won't let you tweak width & height to however way you like because it has strict 'aspect ratio' constraints enforced.
Don't bother, I have one of these & play tested it. Not worth it. Better wait for a hardmod &/or softmod option for your troubles.