The motherboard I'm using has 2 M.2 slots, positioned so that one side of the M.2 card is the motherboard and the other is the edges of multiple PCIe has cards. That doesn't leave much room for a heatsink, but they fit very well. Alignment means the airflow goes over the short edge of the M.2 cards. Since this heatsink does not have solid fins, air must flow through all of the fins. Temperatures are around 32 C in standby and 65 C after 15 minutes of continuous hard work, which is low enough to avoid throttling.