Is the guidance on the inverted vent top being avoided different from that of other gases, or is that applicable across the board?

We are not certain what an inverted vent top is. If this means the hydrogen flow is pointed downward in any way towards grade, then yes it must be avoided. Less dangerous vent gases can be pointed downward, especially those that mix with air rapidly (nitrogen/oxygen/argon). Regardless, reaction forces must be taken into account for any relief valve activation or flow