Sorry, I'm being unclear. Let me rephrase - most cheap H6 TV boxes have fixed CPU voltage. This means that most of the time CPU is powered with excessively high voltage which of course generates more heat. You can't do anything about it because this depends on the chip which is soldered on the board. Contrary to TV boxes, SBC with H6 have adjustable voltage regulator connected to CPU and that allows kernel to lower voltage when lower frequency is set and thus avoid higher temperatures. While SBCs seems unattractive at first glance (plain board, usually no remote nor power supply included), for similar or even higher price, they are most of the time better designed.
But that is already off topic here. Please open new topic or ask in general topic such questions.