I'm just sitting here amused that in Ars Magica we accept that the entire history of mundane politics remains essentially unaltered by the existence of a massive order of wizards and yet we discuss casually reshaping continents to fit our whims.
I expect that destroying a few miles of mainland continent because it is in your way should qualify as interfering with mundanes. after all a typical estate of 1500 acres is about 1.5 miles on a side if it is perfectly square, so how many manor estates are you simply disintegrating to get your island through the straights?