Just curious which is the correct way to install a tension/spring washer that sits between a mower blade and a carrier disc? Concave side up or Concave down?

The Honda manual has an illustration showing that the concave on the carbon steel spring washer (that they provide in their kits) should be concave side down. Yet oddly most Youtube tuts seem to install them concave up.

This is the style of tension washers I'm refering to:
https://www.greenacresmowers.com.au/blade-tension-washer-fits-most-rover-honda-cox-law