Feront turn signal housing left vs right 68 Charger

[tmaleck]

I have the housings for the front turn signals, and they have the same part number. The lenses however are left / right specific. This confuses me. Same housing but different lens side to side. What am I missing?

 

[91r/t]

Maybe the angle of the lens itself is different and fits the lower valance but the backside of the lens is flat and takes the same light housing? On my 68 they look pretty straight forward, but maybe there is a slight difference.