[ldolse]

anything above 0.5 will probably not work. Values that will work are pretty much 0.01 up to 0.5.

That said, I think you may be changing this in the wrong place. The place Dwanthy pointed you too is the global setting - you should set 0.45 under the global settings. However, any time you convert a book it takes the global settings at that moment and hard-codes them for that book. I suspect your book is still hard-coded to 0.0. So start a new conversion, which will bring you to the conversion options for that book. NOW go to pdf input (inside that conversion settings window), and change the setting there to 0.45.

That said, if 0.45 didn't work in the book's own conversion settings there may be something weird with your document. You could open a bug at bugs.calibre-ebook.com for a look. Can't guarantee it will get addressed, a lot of the more obscure pdf bugs are getting punted to the next gen pdf engine, but there is a chance it's a simple fix.