The entire cigar industry maintains their product @ 70% relative humidity...........please explain your claims about 65% humidity......then call Boveda and then tell all the humidor builders for the last two centuries that they had it wrong the whole time.
I have news for you, weed does not mold at 65% RH.
No, but humidity sensors start getting more inaccurate toward the extremes of their range. 2% accuracy is considered pretty good in the mid-range, 70% and on the percentage error starts getting wider. So say you have a meter that is out 5% and you are keeping the humidity at a 70% reading. So you have an actual reading of 74.5%. Then you get the localized humidity at the flower which is 10% higher and you are in mold territory.
As humidity sensors get old they drift. Inaccurate temperature readings can cause the meter to calculate the humidity and report it lower (reading the temperature higher than it really is caused a lower humidity reading). As far as cigars go, they are not giving of moisture that they are sucking up with their roots. If your plant was dead and the plant mass was stabilized at 70% RH then keeping the humidity at that level will not be a problem. But we are talking about live plants. Occasional spikes in humidity are probably ok as plants out in the wild do get rained on. But sustained high RH is looking for problems.
As far as my talk, I can be just another voice on the internet where everyone has an opinion and some are not worth the electrons it takes to get them to you. But I have a background in electronics, I was a Instrumentation Technologist, had my Instrumentation Mechanic Licence (as well as Electronic Licence and Limited Instrumentation Electrical Licence). I have done calibrations on a wide range of electronic and mechanical equipment in a range of industries. I have a good idea of what equipment can do in terms of temperature and humidity control as I took care of those systems for a 30 building hospital complex that housed from surgery to research labs and medication production. The surgeries were shut down at 65% RH do to the possibility of mold, the ventilation system repaired or adjusted to be back below that number and cleaners would disinfect the whole room ceiling to floor.
While cutting open a person might be a extreme condition where you do not want any mold I use it as a benchmark. With my knowledge of the technology and the day to day physics of the air industry I gave my opinion. You might get away with 70% RH and say I am wrong. But the next guy may have 70% dialed in and get mold. It depends on your equipment and your local conditions. I gave a number which I would strive for and be confident that I should not get mold to any great extent forming. I hate tossing out good weed I spent a lot of time growing. I had to toss out a donkey dick from one plant and the plant right next to it was fine. Other than that cola the rest of the plant was fine. So as they say, your milage may vary.
I hope this explains my opinion to your satisfaction.