How to set line spacing between headings; heading and par?

[Andrew15-5]

I've already commented in #159. And till this day there are several definitions of leading/line spacing. But the question is not directly about how leading is defined. I don't see any way to set line spacing between headings and between heading and par. Moreover, these lengths are different by default from what I set up: #159 (comment).

If I were to change one of these length by using negative padding/vertical spacing, the other length would be affected too, so such hack doesn't work as expected either. Maybe there is no support for this yet?