Neat, but the thermal design is absolutely terrible. Sticking that heatsink inside the aluminum case without any air circulation is awful.
The placement is mostly determined by the design of the OCP 2.0 connector. OCP 3.0 has a connector at the short edge of the card, which allows exposing/extending the heat sink directly to the outer case.
If somebody has the talent, designing a Thunderbolt 5 adapter for OCP 3.0 cards could be a worthwhile project.
As a stop-gap, I'd see if there was any way to get airflow into the case - I'd expect even a tiny fan would do much more than those two large heatsinks stuck onto the case (since the case itself has no thermal connection to the chip heatsink).
If that's not a requirement just get the Raiden Digit Light One, which does have a fan (and otherwise the same network card).
If I could design an adapter PCB myself, I would go straight to OCP 3.0, which allows for a much simpler construction, and TB5 speeds.
Alternatively, there are DELL CX422A rNDC cards (R887V) that appear to have an OCP 2.0 connector but a better heatsink design.
If truly concerned, one could use SFP28 to SFP28 cage adapters to have the heat outside the case, and slap on some extra heatsinks there.