Does vertical placement of CRS317 affect device cooling solution in negative way? As in is this semi-passive heatsink optimized for horizontal operation or it shouldn't matter?

based on https://www.youtube.com/watch?v=KNDZZ5bD-wM I would not recommend it. The rear radiator is apparently only element doing some cooling. Inside, there is no radiator at all. Fan's can exchange air as much as they want, but if there is no radiator inside, which would cool the chip, internal airflow might be not enough.

In the end, it will really depend on airflow around the rear radiator. If you put it into small sealed box, it will overheat and it is not going to matter if it is horizontal or vertical.
Radiator is clearly designed for horizontal operation due to shape and angle of ribs in order to make airflow of hot air (coming up) easier.

There are heat pipes inside the case to transfer heat to external radiator. There is no fan on radiator and radiator ribs are designed for horizontal use of the case. You can use it vertically but it needs temp monitoring and perhaps some additional fan for external cooling.

There are heat pipes inside the case to transfer heat to external radiator. There is no fan on radiator and radiator ribs are designed for horizontal use of the case. You can use it vertically but it needs temp monitoring and perhaps some additional fan for external cooling.

I had problems with laptop being unable to cool down in vertical placement (even without any obstructions around) because for some reason heatpipes didn't transfer heat as effectively in different orientations or some other anomaly occurred so I guess it's not worth the risk in the end... Also passive operation is quite important for me so yeah.