I believe those rear feet are primarily to protect the connectors on the back panel. They do, of course, ensure that the back of the unit doesn't press directly against a wall, but it is a rather narrow gap. As long as you're not driving it at minimum voltage and maximum current continuously, it'd probably be OK.
Can you fit it on your bench if it's sitting on its side? Although there are vents on the sides, at least they exist on both sides, so you'd probably end up with better airflow that way than standing on its rear.
If you have a digital thermometer or a DMM with a thermocouple, you could compare different setups with different loads.