Finesse boost can be increased by either increased critical damage boost or increased headshot boost. Increasing critical damage actually boosts the stagger power of headshots and Headshot boost does not, even on non critical hits.
After a series of experiments using numbers from Squattingbear’s statsheet
Chaos warriors require stagger power of 18.6 to receive heavy stagger effects
Greataxe charged attacks have very slightly too little power to heavy stagger a CW on headshot (<5%). Introducing modifiers that increase critical damage allow the stagger, but effects that increase headshot power do not (Any weapon mods)
Testing with other attacks and boosts affirms this interaction.