I just received my Sport, shot it for the first and only time with the iron sights over the Labor Day weekend. Just received and installed a Burris scope on it (3-9x40) and plan to shoot it this weekend. For plinking, I use my MP-15/22 with a BSA red dot.
Both are CA compliant, and together cost me the same as one high end AR-15.
To your question:
Higher than 3X you don't see the front sight (no co-witness). My red dot co-witness, and there is plenty of opinions on how to set it up. I'm still learning, but the most important thing for me is consistency where I rest my cheek, and then everything adjust from there (ring height, and risers etc.). I see many pictures with scope real high and wonder how do avoid parallax.