Ah, sorry, didn't read documentation carefully enough. As for making a suggestion, I can't, because I'm not a modder and it's not a QoL suggestion.
However, one thing I can say is that most deployments in XPZ have custom (not 0 or 100) percentageOutsideUfo value set for each unit, even though it doesn't function. So I can only assume that Dio thought percentageOutsideUfo worked for mission sites as he put some thought into what value to set each time.
Well, nevermind then. Can be closed.