Explaining computers did a quick test last week. www.youtube.com/watch?v=VJC6OpGpq0Y .
I would say however the second device where the heatsinks sandwich the board is a bit of a designers wet dream since the lower half is the most expansive but is not really thermally connected to the board only at the screw lugs to the top.
I prefer the Kodi branded unit since it performed better and totally enclosed the board.
Neither of course are suitable for a two layer stack but give insight into what works best. Use that knowledge to find other similar but taller solutions which no doubt will be available now or in the near future.
Personally I am using the Rock Pi 4 running a DIY Stellarmate install. They have a solution to house their board and an second layer and SSD. Rock Pi 4 sensibly placed the SOC on the bottom of their board making heatsinking much easier.

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