The size of Echinodorus species generally depends upon the species genetics. Having said that, environmental conditions obviously affect growth; this includes the light (intensity and spectrum, less duration) and nutrients.
Individual plants of the same species can grow to very different heights. This again is partly due to the environmental factors, but there may be more than those alone. Adventitious plants (daughter plants) from the same parent plant will often grow to different sizes from the parent, and even each other.
I leave my plants alone once they are planted so they can grow as they wish. If they become a nuisance in one tank, I may move them to another.