"Altitude density" takes three variables into the formula. I do not have a solid answer on which one has more effect on the outcome. My understanding would be that each one has a different amount of effect at different points on the curve.
1. Temperature
2. Humidity
3. Barometric pressure
IMHO the Barometer would be the smallest range of effect. Temps and RH (Relative Humidity) vary by a much larger percentage than the Barometer does.
Temperature seems to be by far the biggest factor in poi shift of my pcps. A rifle and scope can have completely different groupings at 30 degrees vs. 80 degrees.