13th gen does run hot, but it is designed to do so safely. Z790 motherboard may have a default to make the processor run as fast as ti can until it bumps up against the 100c. limit. This is normal operation and fiddling with undervolting will simply reduce your performance. Your aio is probably operating properly since it is new. In time(think 5 years) air will intrude, reducing performance. For best cpu cooling, mount the radiator in front where it can use fresh air. For best motherboard vrm cooling and gpu cooling, mount the radiator on top using inside air for cooling. I would not expect a magical difference which ever way you go.