70% sounds like ideal but I do not know how to manage that in a greenhouse especially in summer. I have to open the door and 4 roof windows to create temperatures which will not fry my orchids. As soon as the door is open I can spray as much as I want and when i am lucky i keep humidity at 50%.
In winter it is more easy for me with automatic spraying the floors 3 times a day and temperatures which do not exceed 22 degrees celcius and no open doors.
My Catts do really well in this environment