Just4growers is a good source, love watching his videos.
Temperature is the key reason RH is not as accurate for water loss in plants, as RH does not measure pressure difference. It measures capacity percentages.
The potential for transpiration will be different with 50% RH at 75°F compared to 50% RH at 83°F. Even though the relative humidity is unchanged, the temperature effects change the potential of fluid movement.
However, relative humidity can be used for a narrow range of temperatures. Outside a set temperature range and the RH can be thrown out the door. Saying that, you are expected to grow within a recommended range of temperatures for optimal efficiency, so the recommended RH ranges can be reliable.
I am going to update the recommended ranges for different stages of growth.