On the issue of the critical moisture content for drying

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I have a question regarding the principles of chemical engineering. In a textbook on these principles, I came across the following description: The drying rate during the constant-speed stage is also influenced by the temperature, humidity, and flow rate of the hot air; reducing the temperature, increasing the humidity, or decreasing the flow rate can lower the critical moisture content. It doesn’t seem right, does it? Shouldn’t appropriately raising the temperature, lowering the humidity, or increasing the flow rate be able to reduce the critical moisture content? The main duration of the drying process occurs during the falling rate period. When the air temperature is lowered and the humidity is increased while the airflow velocity remains constant, why does the critical moisture content decrease? As a result, the duration of the falling rate period becomes shorter, whereas the duration of the constant rate period becomes longer. Is this understanding correct? But why does this critical water volume change? What is the reason behind it? Isn’t there a certain amount of unbound water?