Confirmation bias? Not sure where you're getting these numbers from. Eagles closed -9, Lions -8.5, and Panthers -3. Also take openers at -9 or -1 with a grain of salt given how much books avoid the teaser window.
In reality, it's all moot since this strategy is poorly outdated. Things like RLM, public "money", 'unders' and underdogs are a thing of the past. It's an entirely new marketplace if you've been paying attention the last few years.
It's hard to let go of yesteryear I know. Light a candle and join 2012.