You should zero the ACOG at 100 yards/meters. You can zero the ACOG at 25 meters/36 yards using the tip of the 300 meter aiming point but this is to get a rough zero only, you should confirm at 100 when possible. When using the short range zeroing method, being just a little bit off at such a close distance will magnify the farther out you go.
I zero mine by starting at 25 yard and zero 2" low. That puts me close at 100 yards. Then move to 100 yards and zero tip of red chevron for exact zero. Manual say to zero at 100 yards with chevron tip. That allows the range calibrations to be valid. However those calibrations are for the 855 62 grain miltary cartridge so if shooting any other or handloads the calibrations are only and approximation depending on bullet and velocity.