You need to turn off overscan. This is usually a TV function.
Overscan, in the old days, was used on analog sets to not have unpainted edges of the screen.
Most digital TVs provide a similar function but overscan will make sets with the correct Original Aspect Ratio (OTA) blurrier.
You may need to set the correct raster size 1280x720p or 1920x1080i on a per channel basis.
The 720p is used by ABC, ESPN, and other Disney and most Fox channels and where there are subchannels.
The 1080i by CBS, NBC, and full (non-subchannel) channels.
Your Dish box converts all to your choice and it should m atch your TV's native capability.
There is no pass-through selection. "Non-matching" sets will always be blurrier.
-Ken