Don't think it is a pure space issue
Think about it. Most people have well over 50% of their land occupied with their town layout. Probably close to 75% if you also count the 1 square border around buildings. This would imply that no one really should ever get 2 spawns per day and many would get less than 1. That is clearly not the case. I have a very broad th9 layout that probably takes up 90% of my land and I easily get 2 sometimes 3 spawns per day. I do harvest my obsticles as soon as I see them though so it might be that an area taken by another spawn impacts the ability of another spawn but I don't think buildings play a part in this