I have one of those. I use a very small dab of MX-4 and my CPU is at ambient at idle.
most use far too much thermal material
In my Obsidian 750D, my H115i is mounted in top, fans push air up through the radiator and out the top grill. The radiator itself is attached to the top of the chassis. The fans are attached to the radiator. This is the most common configuration.