This is probably in the rules somewhere but I couldn't remember offhand - again with scenario 3 - blood ties, there is a large outdoor area, and several spots where tiles match up such that there is no obstacle to moving diagonally.
It is in the rules. For a change (for FFG rules that is) it is in a more obvious place
Page 8 Movement Step.
Investigators may move between two spaces that are diagonally
adjacent. Due to imperfections in die cutting, if spaces between
two tiles appear that they should be diagonally adjacent, then they
are. All non-adjacent spaces very clearly do not share a white
border by at least 1/8 of an inch.