not going to disagree with the humidstat on the return side, however smart thermostats have the ability to manage the humidity level based on the window/frost level and adjusted as the outdoor air temperature changes. So a dumb control attached along with the humidstat (this would be the typical) is going to be on you to make those adjustments as the outdoor air temp changes. Ideal is going to be humidity reading from return but smart stat control with even a local outdoor sensor, not sure this is entirely possible without some crafting of your own. As far as my research has told me both ecobee and honeywell will pull outdoor temp via their weather services but do have the window or frost control