Most likely the side nearest the Exhaust is getting a "second dose of cooking" when the combusted gas exits the chamber.
Be grateful your where you are. For a while, my plugs came out Rich as hell. So rich that I could hold them up right, light them, and use them as a candle.
member number 684
71' coupe project:
goal: 150+MPH, 9s driven to and from track, 275 front tire, 315 rear tire, 1000+HP
Build: 540cid, twin turbo, 4L80e, ...wait for it...
Heart of Dixie Chevelle Club