I advise against other card directly below the "heater" insert as electronic components great heat not usually like.
Even if you allow enough space down you should still remember that the card may all surrounding components on the main board heated in which it is inserted.
My tip:
- Either a fan under the radiator stick (for example with epoxy resin adhesive.) But then comes more space lost.
- Other graphics card purchase either does not heat up as much, or already has a fan