MFD Hot, heater question

It was overcast today and the temperatures were mild, with a maximum of around 72F. (Climate control is set to 68F.) First we went to a toxic waste pickup, which involved a 15 minute highway drive, followed by a very slow crawl of 15 minutes more in the line, then a 10 minute drive, and 20 minutes parked while we shopped. The car was "in the sun" for all of this, usually with the windows down and the cabin fan off, but the sun was always behind clouds. Shortly after getting in the car to go home my son happened to notice that despite the lack of direct sunlight the dash above the glove box was warm. After a bit of pawing around it was further determined that the entire top of the dash was equally warm - except the area immediately above the MFD, which was very warm verging on hot. We assume the general dash warmth was from IR that came in through the clouds, but that doesn't explain why the MFD was so much warmer. I don't recall ever bothering to put a hand on top of that unit except when the car had been off for a long time, for cleaning purposes. Does a powered up MFD normally generate a lot of heat? This is the low end model, no navigation or rear camera. Since electronic/electric devices on the way out sometimes run abnormally hot I am trying to determine if that is what is happening here, or if this level of heat is nothing to worry about. (It doesn't seem likely that the MFD would somehow be warmed much more by the sun than the neighboring parts of the dash.)

Which brings up another question - how does the Prius regulate the amount of coolant passing through the heater core? The service manual notes that there is a pump in the ICE coolant loop which is used to circulate coolant when the ICE has turned off. Our Accord has an inlet valve for the heater core, which it opens when heat is needed. Does the Prius also have such a valve? If not, does it control cabin air temperature by one of the air mixing actuators alone? That is, if the car is on will the heater core always have coolant circulating through it, even if the temperature is set below the ambient temperature? (I know there are also electric heating elements.) Also, is the heater core directly posterior to the evaporator (there is a diagram in the service manual that looks like that), in the center console, underneath the radio and MFD?

Thanks.