A breakthrough today. I realized that one doesn't tell the slicer/gcode generator what you want the bot to do, rather you tell it what it can do.
So rather than the setting "extrude speed" be saying how fast it should extrude, it says how fast my machine extrudes. So if not enough stuff is being deposited, I have to lower the value rather than raise it!
This is a huge deal. Now I can make prints very tight!