Your final sentence is very unnatural. Not only do we normally say "I sit on a chair" (not "upon"), I can't imagine any situation where I would say "within the back row".
Hmmm, I thought I was responding to a question regarding personal preference, not specifically clarifying a grammatical rule.
What is unnatural for some, may not be for others. Someone who has been educated and trained for stage performance, for instance, may speak with a different tongue. Perhaps someone from certain areas of England, or South Africa would speak in what may seem an unnatural manner to you. Yes?