The Arma series is marketed as a military simulator, so certain things in the games are semi-realistic. In this case, the physics you're referring to may very well be the cause (at least for the assault rifles). All of the rifles will be shooting over their indicated center point until about 100m away (SD weapons not included). Without getting into zeroing/ranging the weapon, you're bascially observing the bullet's trajectory before its traveled far enough to experience any drop. Thus, it hits high. You probably knew all of that already--my apologies.
This is all very general and is certainly not universally true, but it is something to keep in mind. The handguns shouldn't experience it nearly to same degree as a rifle. All of the sights work differently, but with the PDW SD, I think you want to put the target (in this case a zombie's head)
behind the post of the sight as opposed to just above it. The sight would obscure the target slightly in this case. Some iron sights just aren't that great.
