Crosshairs not turning red

I am new to halo 4 (not the halo series) and thought that my skills were just a bit rusty until I noticed during the “kill sequence” that my enemies crosshairs turn red far sooner than mine, and much further off target.

I have been experimenting over the last several days, and noticed that I cannot get the crosshairs to turn red until I am less than 5 feet away, REGARDLESS OF THE GUN! Even at a stand still, scope drawn and my enemy in dead center of the crosshairs, they will not turn red. WTF! I virtually have to give up trying to shoot someone, and run at them full speed to attempt a melee.

Am I missing something here? That seems weird right? Is there a setting or a button that I am supposed to push that’ll “lock” onto my target?

Frustrated.

Kill cams or whatever 343i are calling them aren’t exactly reliable.

Regardless of what you see in said kill cams, every player’s reticle will go ‘red’ at the same distance (depending on different weapons of course)