Laura,
Beenthere is correct that using the Dry function is rarely needed. I know you are concerned about the humidity as much, if not more, than the actual air temp. They do go hand in hand to a certain extent.
Since the system will have an inverter compressor, it will set the compressor speed so that it is cooling at the rate the space is gaining heat. This means the compressor will be running almost all of the time, and thus, providing de-humidification on an ongoing basis. Thus, sizing the system correctly will be important for it to function best.
Most mini-splits do not monitor the temp when in Dry mode. The way it de-humidifies in Dry mode is to slow the indoor fan to the lowest speed and then run the compressor for a few minutes at a time, cycling it on and off. It will continue to do that and if the space is not gaining heat as fast as the space is being cooled, then it will get over-cooled.
The best way to condition the space for comfortable humidity is to keep it conditioned on an ongoing basis. By keeping the space conditioned throughout the day it will help keep it conditioned through the night. This does assume the home is not like a piece of Swiss cheese and can keep the cool dry air in and the warm moist air out for some reasonable period of time.
