Concerning the issue.....
Just to compare...... If ADE is used as eReader program, then zooming in increases the font size but it does not affect the page width. If in a smaller size 20 words were on one line, then after zooming, 14 words are on that line, the page width is kept. That also is how it is handled at an eReader. It means that the amount of pages of an eBook increases this way.
In the classic view of Sumatra I can resize the font, but it also affects the page width .... the same 20 words are kept on the one line, and to see them all I have to scroll horizontally.
But if this fixed page width with less words on a line is not possible in Sumatra, I assume, I have to use ADE or the Calibre Reader, although I would prefer Sumatra because of its good PDF handling which isn't good in ADE.