I just dug up a scope with a 3-9x magnification. It is 12in long so it looks a bit goofy on my Ar-15 M4. I was wondering what is the difference between long scopes and shorter tactical scopes with the same magnification. I know the ACOG has a 3x zoom and a very low profile, but can't zoom in greater than 3x. I feel almost like if I'm not going building to building having a longer adjustable scope is more of an advantage. Any input?