My background is black so unless you are at the tank looking you can't see mine. But I have it horizontal and right below the HOB
and next to the spraybar of my canister.
I figure the heated water will be pushed down and across the tank by the current this way. I keep it near the top so its easier to change temps if need be.
Also the visitherm stealth heater has an automatic shutoff when the water drops below the minimum water line. I actually haven't tested this option. I'm like severum mama, all my stuff is plugged into the power strip, except lights. That way when doing a water change I only have to flip 1 switch.