It may be a linear scale, in that 0.5 is half-dead, but the effects tend to be inconsistent and unpredictable. My guesstimates:
Up to 0.1 - probably unnoticed, aiming unaffected
0.1 to 0.6 - reasonable range for your purposes - the annoyance is the display of wound textures
0.85 - start suffering leg wounds - forced to crawl or body-pop (stand-up, run, scream, fall over, repeat)
0.95 - immobile, won't even crawl
For the early stages, you might want to try "blah setDammage -1" (either spelling Damage/Dammage should work). This should give the wavering aim of being wounded, but without any other effects.