When you place a foundation, it automatically makes the top of the foundation flat with the terrain or ‘earth’, and just extends the bottom of the foundation, as needed (within limits), to allow for the foundation to be placed on uneven terrain, but at the same time ensuring that it is flat on the top.
If the farming plots were paced the same way, it would make for a much more astatic look instead of everyone’s farms looking like a complete mess. Even if the limits on how tall the farming plots can be were greatly restricted in comparison to the foundations, at least I could make a tidy farm area. It would be even better if the plots would ‘snap’ onto foundations/floors if they were low enough to the ground (The way foundations snap onto each other).