All ACOGs with BDC are designed to be zero'd at 100m.
The primary aiming point -- in your case the crosshair -- is 100m zero, then the bullet drop ranges underneath work. The large illuminated line is 300m (and the width of the strada is meant to be 19" at 300m, e.g. the width of a man's chest), then each other is marked down from there -- 400m, 600m, 800m, 1000m, etc. Each spot is meant to be "minute of man" at the appropriate distance.
Edit to add: these examples are with the classic ACOG chevron reticle, but the same thing applies to the crosshairs: