Ok, I took the plunge and picked up my first AR-15. I've never used a six position stock before and am wondering how I find the optimum setting. Fully collapsed is obviously out, but fully extended and five clicks out both feel natural when using the irons. I'm only 5'7" and my arms aren't on the long side. What determines the best fit? Eventually I'll throw a scope on it. Will that necessitate changing the stock setting?