Horizontal AIO system
Horizontal AIO system
You're wondering if flipping the AIO vertically might affect cooling performance. Your test showed a 11°C improvement when mounted horizontally, so it seems the orientation matters. Keep experimenting to confirm!
This setup isn't quite right, since you want the top of the loop to be the highest point for air bubbles, but they'd end up at the same level as others.
The main point to remember is that the aio must be positioned above the pump; otherwise, it may not last long. A picture would be very useful. It might simply be because your situation involves extremely turbulent airflow, and adjusting it provided more space for breathing.
The pump should not be positioned at the highest point of the AIO loop. Adjusting the computer's angle shouldn't noticeably affect performance. I also expect you won't block airflow through the intake and exhaust ports. Back in the day, heavy hard drives and CD trays often caused computers to boot only in one position. Today, with SSDs, you can handle almost any orientation without problems.
Which situation are we discussing? It seems you tested without the side panel, which likely caused the variation.