Unfortunately, the legacy at Dish has been that customers complain vehemently if fans are running in DVR units. This goes back to the 721, and I think ever since, Dish has been resistant to place the fan at the rear as opposed to the bottom of the unit and will do almost anything from having the fan operate. People had complained to Dish about the fan running in their bedrooms and losing sleep and always tiring of hearing it in the living rooms. The complaints were voluminous. Eventually, Dish set the fan to NOT turn on until a much hotter temp. Customers happy, but 721's would overheat. Then Dish sent update to prevent 721 from doing too many things at once, which would have the effect of heating things up with process intensive tasks. They seemed to have found a happy medium and 721's did not overheat (unless in a confined space and not enough airflow at the BOTTOM of the unit), and the fan just never seemed to kick in anymore.
Meanwhile, my TiVo's run cooler with the fans at the rear making spacing above and below the box not at all important, but you do HEAR THAT FAN whirring (both S3 and S4) day and night and sometimes LOUDER than the more quiet passages of movies, but I appreciate that it is on ALL THE TIME to keep things cooler. TiVo owners seem not to complain, but Dish subs have complained to me back in the years when the fans were very active, and just recently, someone complained about the updates always waking him up at 3AM--you know, the short fan high-speed for a few seconds--GOOD GRIEF! I was amazed he was that light of a sleeper. That update noise doesn't come close to ever waking me up.
My point is that the Dish legacy and "culture" is that active cooling fans, even at a modest speed (that trick was tried with the 721, but they eventually just shut it off unless it got terribly hot) creates complaints. so it seems Dish prefers to have the devices run REALLY HOT compared to cooling with a fan that generates complaints. Now, why don't they provide MORE vents to compensate? It seems like they put this stuff in boxes that are almost solid. The IRONY!