The IR sensors pictured are proximity sensors ,not break beam sensors. They work basically with opposite principles: break beam reacts to the absence of a beam because it's blocked by an object that's in the way; the proximity sensor reacts to the presence of IR light as it's reflected by an object in front of the sensor.
With those bags I think the first will work better: if the beam is reflected away, the proximity sensor will still not see it. Experimentation is needed, for sure.