There is no such "rule of thumb." Don't try to make shit up and expect everyone to buy it.
Buy this, dumbass, the author of the phrase, "subject to the jurisdiction thereof," Sen. Jacob Howard of Michigan, made it abundantly clear during Senate debates that it does not apply to alien children:
It excludes not only Indians but persons born in the United States who are foreigners, aliens, [or] who belong to the families of ambassadors or foreign ministers.
Likewise, Howard’s co-author, Sen. Lyman Trumball of Illinois, said that the phrase meant complete jurisdiction:
not owing allegiance to anybody else.
Allegiance. French a-legiance, homage. Latin ad-ligare, to tie, bind. The tie, or ligamen, which binds the subject to the king in return for that protection which the king affords the subject.