The most recent example I've seen of this was a TFU sniping on top of a fence that is extremely thin(the one near scrapyard that overlooks projex), technically speaking I would say this is breaking 3.3 as such a fence would not be stable enough to hold a big ass man with a sniper and even then should this fence hold the person I doubt he would be able to snipe comfortably.
Attempting to reinforce a rule as subjective as this one might lead to plenty of gray areas that will lead to headaches for both staff and users, I wouldn't know how to solve it though.