Small plot has more usable yard space than a medium plot.

[Nihility]

Perhaps FC plots are different than personal plots, but there's no way a garden is fitting on the side areas in my medium house.

it's the house model.
some like carbuncle and the castle are huge.
and others like paisa are much smaller

if you don't want to use the more advanced furniture placement techniques you can always swap out your house for a smaller one to place them then swap it back