I was joking don’t worry.
To that end though, it sounds like you’re saying just throwing one of these AP In the middle of the middle floor would probably be sufficient to provide wireless access to the whole house.
And as you have correctly assumed, internal walls are plasterboard (I think it’s maybe called something different in America?) with metal studs. But the floors(?) between floors(?) are concrete, besides the 2x2 holes that the stairs live in.
I knew you were!
With concrete floors, one AP/node per floor
may be needed (depending on the actual/specific floor).
Build this network slowly, don't assume 'theory' will translate directly to what will work 'practical'.
Even with concrete floors, I would consider a (slightly) modified version of the suggestions in the link below.
AiMesh Ideal Placement
If you wanted a
wired backhaul AP/node on each level, the following is something to consider for the best coverage, and most reliable/stable operation (and more ideal client roaming) too.
This is looking at the entire area you wish covered from a side view of the long side of the home:
AiMesh router----------------------------------------------------------------------------------
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AiMesh Node-----------------------------------------------------------------------------------
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-----------------------------------------------------------------------------------AiMesh Node
Ideally, each node would also be diagonally opposite the router/node above it, on each level.