The technical term in describing the difference is that they have a larger soundstage.
In laymans terms lets say a cone speaker reproduces the sound of a cat's meow. The sound received by you to be would that of a 1ft. tall cat. The sound reproduced by a planar speaker, since the speaker has more surface area, would be that of a cat 4 ft. tall.

This is just my opion and I am not an expert by any means.