Without getting too technical, it seems that an optimal antenna height would have to be relevant to other antennas nearby. That, and ham radio signals are not going to be as strong television signals, so your antenna is going to have to compete with them somehow.
Indeed, you have put it forward in a very simple way. I think that explains why it is difficult to get a good signal in some areas because of a lot of antennas nearby.
It is also now clear to me that ham radio signals compete with television signals, so it means that you have to consider several other factors, of course apart from the antenna size.