Well, even if there's no scope... when you're at the extremes, going more extreme in that direction results in no further penalty but you get the bonus.
Say the AK-97 had no scope. Whether the AR is 1 or -3, either way its the same result (defender gains edge) except taking the burst fire gives you +2 free DV. Unless the attack flatly isn't possible at AR-3. OTOH if the AR was high enough to to still be a positive number after applying the -4 penalty, then the starting AR had to be 5 or higher. And at that point, we're not in "extremes becoming more extreme". AR 5 means you are still denying edge to a reasonably sized envelope of possible DRs. Going down to 1 means you're all but guaranteed to give away edge, so the "price" of your +2DV is "working". It stops "working" when you start super low, and then go below zero.