The fact that you do that instinctively is admirable Michael. When you meet a prospect for the first time you want to establish rapport and trust. As human beings we tend to like people who are most like ourselves so you do want to adjust your style to match your prospect.
If someone is a laid back, even keel type of person and they meet an aggressive, energetic sales person they tend to feel very uncomfortable and it's hard to establish trust when you get a poor first impression. You can probably think of a time when you were personally a prospect of a sales person and experienced it yourself. Think about how you felt?
We recommend you do your precall planning and determine if your prospect is high energy or low energy. Then determine if they are an informal or formal person. I have had success in asking their assistant or receptionist before I leave the office. By getting that information it helps me determine how I will structure my first meeting for the best chance of success.