Honestly, I've never spoken with 2/5 people who wrote my LORs. They were both professors I had in previous years and I just emailed them randomly with my resume and asked if they wanted me to answer any other questions. Of the remaining 3, one was the dentist I work for, one was a professor of a small class and I met with once before he wrote me the letter, and one was an established professor whom I actually went out of my way to get to know before I asked him for a letter. Don't overthink it. Just be nice.