Either that or severely penalise outliers.
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The idea of enemies on the side being damaged more if they're far away is weird. Maybe a unique shotgun (the jackhammer, maybe?) could work like this.
Actually those numbers come from applying a gaussian distribution formula to the angle of exit and adding a range dissipation penalty. That's what the small spreadsheet i linked above does.
I perfected the range dissipation formula to calculate cumulative loss % over distance traveled, so now it looks a bit different:
Standard Deviation: 0,15 rad; Dissipation: 8% per square (shotgun)
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Standard Deviation: 0,3 rad; Dissipation: 16% per square (double shotgun)
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@8765443222
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Edit: I removed the ones to make the spread look cleaner.
P.S. - Yes, the spread is absolutely ludicrous, but like Malek said, it's what you expect in a video game. Shotguns wouldn't be fun if they didn't hit all over the place.