Not sure why I’d need foam. I just cut out notches in motherboard tray so I can keep the motherboard mounted flat as possible, and to be able to remove the back mount plate when I delid.
Its an older direct die trick to make sure A: you get good mounting pressure and B: You don't damage your die
It appears EK did a good job in dialing in the mounting pressure so your CPU doesn't get damaged but from what I've seen so far, that means the mounting pressure is not great and there are some grumblings about temps.
Using a foam weather strip (something like
THIS), attach it to the capacitors behind the CPU die, just thick enough (for my 8700k, IRRC, I used two 1/4" or 1/8" thick foam layers) that you can feel resistance pushing up form the back of the CPU die, but you can still easily place it into the socket; you don't want too much pressure. Anyways, not required but certainly a recomendationg. If you are interested, I will be selling my 12th Gen Supercool DD block, probably this weekend. From what I've seen/read, its about 5-10*C better than the EK DD block (and doesn't require the foam as its mounted the same way you mount an IHS.
Here is my best MSPaint representation (black is the CPU and green is the foam):