Oh my god, WHAT? That signpost thing sounds sooo insanely useful. I have to think of ways to strategically place every tile and PWP so there's no 3x3 empty plot, it's quite the pain lol
- - - Post Merge - - -
I went through and put patterns and paths everywhere in hopes of controlling where I wanted epona to put her house, I’ve had enough luck with it in my other town but for some reason she was allowed to plop her house down in the middle of my paths

I was almost certain they couldn’t plot on paths or patterns on the ground in the welcome amiibo unpdate but I guess not ;-;
They will only do this if there's no other place for them to move. So you must not have had an empty plot section, and if you did, perhaps it was to close to a rock, river, PWP, house, etc etc.
I've covered my ENTIRE town in a basic path when I reset my town. So far I've had 7 villagers move in , and each one landed in the 3x3 plot I had empty for it. Nothing can be placed around that 3x3 plot, meaning another house, PWP, etc. If two houses are side-by-side, there must be two spaces between the 3x3 plots.
PS. And remember that each house has an empty square in the front of the door (commonly labeled "D" for door), as such:
HHH
HHH
HHH
. D .
You must have at least one empty space in front of the door, as well. So if you are building houses in a vertical row, there must be 3 empty spaces between the 3x3 plots.