Humidity

Try to get your VPD around 1.0-1.2 for early flower Dont worry about mold until your RH reaches like 70%+ and/or you got no airmovement in your tent.

60% humidity is perfect during flower

1.5kPa is probably a bit higher than what is actually occuring at the leaf (around stomata on underside) unless you are using an infrared thermometer and measure multiple locations throughout canopy to average it out. Also, placement of the RH probe will impact calculated VPD too. This is fine. You'll need to observe and adjust based on plant growth to figure out what is optimal relative to your local variables and how you measure them etc.. Even the concentration you feed at is impacted by VPD. A higher VPD needs a lower concentration because it increases rate of water uptake.

Greater than 65% is more often associated with increased microbial growth. As long as you dont hit dewpoint as temps drop after lights go off, you are fine. RH% should jive with temperatures and 55% is often a good range. Refer to a VPD chart (vapor pressure deficit). Leaf temps are 3-5C lower than atmosphere readings. RH% is higher around leaves, too. Things to consider. I used to have a problem with wpm. I checked my RH and it always seemed okay, but what i didn't know was that as the temperatures dropped at lights out, the RH was rising faster than my 50-pt dehumidifier could handle. So, i was consitently causing dew on my leaves -- even if only for 10-15 minutes before circulation fans helped evaporate and dehum caught up. I keep a much wider birth away from dewpoint during this transition. I know my dehum can only safely keep up with 36-40sq ft of canopy. 40-65% is relatively safe on its own. The dewpoint is your enemy more than anything else. Because of the leaf temperature and higher RH in canopy, keep a sufficient gap between atmospheric temp reading and calculated dewpoint. A wireless temp/RH probe is really useful for a dark tent you cannot enter during flower phase.

Yes, go to VPDchart (dot com) input the RH, leaf temp, and room temp. It will tell you the ranges and everything.