I am confused about rejection of the below edit:
I can understand that the question is about casting of a movie. However, the OP seems to be explicity interested in romantic movies. In fact, if we consider comedy movies, there is very much change where we will find couples with different heights just for fun.
So I want to understand if it is not good practice to tag questions with genre tags when it is specifically asked by OP for the same. There are certain people who are experts for a particular genre.