How much do we believe those in casting select contestants with the idea in mind that certain people will "match?"

This season in particular, I noticed people with similar personalities and also people that I think could have easily "hit it off" with others from other couples. It got me thinking about how much those in casting might be purposely selecting people they think will "click" vs. just picking the most interesting, eligible, good people? We all know they include people that start drama to keep the show interesting, of course. But I am starting to believe they may even have this secret "diagram" where they pre-plan out who they think would match or work, and purposely select people based on the possibility of many of them working together specifically. Thoughts?