papaja: modify spacing under headings

I am using the package papaja to write an APA-formatted manuscript with R markdown.

I would like to modify the default spacing under headings (it's presently too large for my taste). As shown on the sample picture below (document rendered as pdf), spacing around the headings is more than double spacing.

I've looked at different solutions, including the \raggedbottom option in my header or the latex function \titlespacing from the package titlesec (https://tex.stackexchange.com/questions/53338/reducing-spacing-after-headings), but I haven't been able to make it work. I'm a newbie when it comes to Latex.

Below is my current header:

 header-includes:
  - \usepackage{dcolumn}
  - \usepackage{setspace}
  - \AtBeginEnvironment{tabular}{\singlespacing}
  - \AtBeginEnvironment{lltable}{\singlespacing}
  - \AtBeginEnvironment{tablenotes}{\singlespacing}
  - \captionsetup[table]{font={stretch=1.5}}
  - \captionsetup[figure]{font={stretch=1.5}}
  - \raggedbottom

Note: I hesitated between posting this question here or on the Stack Exchange - Latex forum. But because of R markdown and R package papaja specificities, I decided to post it here.