I personally have not put much thought into VPD I’ve always payed more attention to PAR but I will try anything that might help improve my grows. According to the chart I’m about 25% off and should be around 75% right now so I’m getting a humidifier tomorrow.  I think this is an interesting topic. I do believe VPD playes an important roll, maybe even more so in DWC, however I also think the size of the plant matters as well. Vince your grows are always solid, but I have noticed when they get bigger than your normal grows seems then you loose a little control of the environment. I know what my issue is with my environment and it’s not terrible but nothing ventured nothing gained.