This video demonstrates the effect of light-curing a composite disc that is the same size as the mesio-distal dimension of a mandibular molar for 10 s with a small and a large tip curing light.
Note that the small light tip does not fully cover the composite.
After immersion in acetone, the small light tip does not cure the composite very well beyond the light tip. This happens both at the top and bottom.
So you must deliver at least 3 exposures using the small light tip to fully cover the composite with light.