Here is a picture to give some details on EOTech EXPS3 / XPS2 Adjustment clicks are 0.5 MOA or 1/2 inch at 100 yards 0.5 MOA @ 50 yards =1/4 inch ......
0.5 MOA @ 50 yards =1/4 inch
An average sized man standing 5'8" will fill the 65 MOA outer reticle at 100 yards. Same man will fill half the reticle at 200 yards, and 1/3 of the reticle at 300 yards.
Having an understanding of your optic and its relationship to a known size will help you with range estimation.
Take a little refresher using google-fu look up mil-dot math or check out a sight I have found invaluable :http://www.mil-dot.com/