Probably you've read the wrong documentation.
The HP ProCurve 1810G-24 Switch (J9450A) Installation and Getting Started Guide (see here) reports, among others, these very first explicit warnings:
- The rack or cabinet should be adequately secured to prevent it from becoming unstable and/or falling over. Devices installed in a rack or cabinet should be mounted as low as possible, with the heaviest devices at the bottom and progressively lighter devices installed above.
- When wall mounting, to meet national and international safety requirements, wall mount either with the front facing up or down. The side vents cannot be placed up or downward.
So you should be OK with regard to placing it with its ports facing downward as you need.