Mine's only slightly larger than that (mostly by virtue of having 3.5 levels, not by X-Y size), but the original plaster walls attenuate the hell out of 5GHz signals. I have two APs, one in the basement and one on the second floor and even with that, I'm considering adding two more inside and a dedicated one outside to serve the patio/BBQ area as I can readily tell the speed difference to internal file and backup servers if I'm in the same room as an AP vs on another floor or outside.
Make no mistake, it still "works" with just one, only slower.
Somehow I have managed to spend most my time in a house that has concrete and brick stopping 5G, a house with wooden walls that block RF and foil insulation under the floor which is even worse, and a workplace environment that has literal faraday cages all around.
I like UniFi in wall access points in the room I’m inside.
Make no mistake, it still "works" with just one, only slower.