I don't think there's any option. Based on where you have the figure reference in the text (near the end of the first page), the figure cannot go on the same page after it, so it's forced to the next page (which happens to be in the references.)

I am not sure what you mean -- the figure is added just after the 'Summary' heading

# Summary

![Relationships of common functions as implemented in PsychroLib. Bold arrows show the relationship between function involving a direct call while light arrow show the relationship between two or more. For a complete list of functions available in PsychroLib, see the README file in the project’s repository.](psychrolib-relationships.pdf){ width=20% }

see: https://github.com/psychrometrics/psychrolib/blob/7d58638002f2bf6046d745a131ceeecc895a84d4/paper/paper.md

Is there a way to force verbose output?

Figure placement in pandoc is a black art as far as I can tell.

I've just tried the following @dmey and it produced this pdf:

# Summary

![Relationships of common functions as implemented in PsychroLib. Bold arrows show the 
relationship between function involving a direct call while light arrow show the 
relationship between two or more. For a complete list of functions available in PsychroLib, 
see the README file in the project’s repository.](psychrolib-relationships.pdf){ width=90% }

Doing a quick search I got to jgm/pandoc#845 (comment) where it may be enough to override the fig placement but not sure if this is something you are looking to change in general.