Line Height (Tibetan font) EPUB to PDF

[ncs]

Hello everyone. I am glad to come across this site and the conversion tool.
I had to convert some Tibetan ebook (EPUB) to pdf and only Calibre has managed to do it very well.
However, when I convert the document the line spacing remains the same (quite big, hence big gaps between the lines). I tried 'fiddling' with all parameters in the 'Look and Feel' section without much success.

Any suggestion would be greatly appreciated.

I don't know the HTML or CSS language.