Iirc Avalon is on the "outside" of the doughnut shaped plane that is what we call the world
But technically from an outsider perspective the doughnut shaped plane of Avalon is within the doughnut shaped plane of "the world" which is inside the doughnut shaped plane of the land shadows.
And Solomon burns from the outside in, so Scathach is dead cuz Land of shadows burned up already, but Avalon wont burn until after Chaldea fail