I just checked:

On an 8x10, I have 1" hi x 1.5" wide; on an 11x14, I have 1.25" hi x 1.75" wide.

It kind of depends on how thick the lines are... Too thick and too close together...it's visually distrcting.
Too thin and too far apart...it's hard to see the pattern and judge things.

Another reason for using a focusing sheet instead of focusing directly on the easel surface: if you use a precision grain magnifier you need a piece of paper of the same thickness as your printing paper under the magnifier. Otherwise your plane of focus will not coincide with the papers surface.