[Skydog]

Originally Posted by theducks

This is a (mostly) empty paragraph (or forced Break) that some use because:
1)They don't know how to us top/bottom margin values
2)Their device ignores margins used in #1

The problem: is these margins are indistinguishable from Scene breaks, Header spacing and a host of other uses.

IMHO trying to sledge hammer fix with Calibre is asking for a mess.
This is a case where a EPUB editor like Sigil is handy.
first)
Replace the desired cases with a new selector to distinguish these.

class="x2TTLPG-AU" -> class="scenebreak"

all you need to do in the stylesheet if no other properties need changing

.x2TTLPG-AU, scenebreak

is add a comma and the additional selector to make a group
next)
adjust the top/bottom margins for those other styles that spacing is desired

Now you should be ready to remove those other 'empty lines')

Thanks, theducks. So, If I edit the stylesheet as you've described, followed by an ePub => ePub conversion removing unwanted line spacing in the body, this will keep the others (TOC, chapter headings, etc.) unaltered?

The odd part of my problem is that the original is fine -- it's only when sideloaded to the Kobo that the extra spacing appears.

I am new at this and learning.