No the ACOG has a backup Iron sight on the top which is quite clearly visible and has been since Arma2 OA, and there is an option in the game to use the sight option (IE Numeric keypad "/").

You should not need to carry multiple sights when the sight you have has the ability to perform both.

I think normally adding ACOG removes iron sight. So when adding ACOG your not able to see through iron sight anymore...

-> You also have iron sight in your inventory instead of ACOG

@Geez You can confirm this ticket, as it is very old, but is being reproduced now. This is not a proper use of the ACOG scope features.
This part of the sight is not activated on any rifle.
On the M4, for example, where the iron sight is removed to install the ACOG optics, only the ACOG optics work, and the switch to the ACOG iron sight does not occur.
On sg5k with ACOG, switching to an iron sight shifts its eye to the sg5k iron sight, which leads to a poor view of the target.