The temperature of the water affects what kinds of flavors you extract from the grinds. Boiling water is too hot, and over-extracts the coffee, leaving the final cup with unpleasant bitter notes. If the water is too cold, it under-extracts your grinds, and leaves you with a bland cup and sour notes. 

 

 

After coffee is roasted, the beans release carbon dioxide, which is called "degassing." After the beans are ground, the degassing happens even faster. This process is further accelerated when the grinds come in contact with hot water. The blooming step helps the carbon dioxide escape into the air, rather than going into the coffee. Carbon dioxide leaves a sour taste if it gets into your coffee, so blooming helps you brew a smoother, less sour cup.

 

 

If your mug is deep and tall, the pouch sits above the coffee level in your cup throughout the whole brewing process, so the hot water is only extracting from the grinds as it drips through the pouch. However, if your mug is smaller or shallower, then towards the end of your brew the pouch is sitting below the waterline of coffee in your mug, which means the grinds are getting immersed in your coffee, and you will extract a bit more flavor this way. Neither is better or worse, but you will likely get a stronger and slightly more bitter cup if you use a smaller mug. Check out this blog post for more info!