I understand your question, but I'm not sure if you mean in Act 1, scene ?, or Act 2, scene ?. It's important when you ask questions like this to be specific about both the act and scene number so that the eNotes editors can be of more assistance.
I would say, though, that the differences between the pairs - Hero/Claudio and Beatrice/Benedick - are established right from the beginning of the play. Hero hardly has anything to say, and it's up to a director if they're going to have her noticing Claudio much from the beginning or not. We kind of assume they know each other and are twitterpated by one another because of Claudio's words to Benedick in that first act - "Can the world buy such a jewel?" when he is speaking about Hero. Then in Act 2 we find that he is so crazy about her that he is jealous and angry when he thinks Don Pedro is actually wooing Hero for himself, rather than for Claudio like they agreed.
While all this is going on, Beatrice and Benedick have already verbally sparred with one another, both of them claiming that they have absolutely no interest in ever falling in love or having someone fall in love with them - (Beatrice) "I'd rather hear my dog bark at a crow than a man swear he loves me."
The point is that Shakespeare established the differences between these two couples early on, and continued it throughout the play.