Chinese characters, when written horizontally rather than vertically, are written without spaces (in unicode there is a character that looks like a comma and includes a space after it as part of the character). The html converter does not know where to put breaks so in parallel mode the longest line dictates the width of the column. My wife reads Chinese traditional characters and says spaces can be inserted between characters, however, for copying and pasting into a powerpoint, for example, all those spaces would need to be deleted. I think the best approach may be to insert a thin space :   or   OR hair space :   following every punctuation mark (the Chinese comma character includes a space as part of the character) so that any line that has a punctuation in it can break at that point so that in Parallel mode in e-Sword the width of the Chinese column will be the longest segment between punctuation in that chapter.
I expect the same may be true of Japanese kanji and perhaps Korean, in short, any east Asian writing that does not use spacing as a clue for the html code reader that it is OK to break the line.