More often than not, "cover" images (first spine item in the reading order, full-page picture) cause excess blank before/after

[danielweck]

...or in some cases the image is split across CSS column boundaries :)

I need to document actual test repro cases with Thorium. Will do when time allows.

In the meantime:

https://github.com/edrlab/thorium-reader/issues/1861

[danielweck]

Related discussion https://github.com/readium/readium-css/issues/119