Significance of hand placement in forming mudra
Short Answer: It doesn't matter.

Long Answer

Some postures are said to be more conducive to concentration, and perhaps this is true to a certain extent.  Perhaps there is something with certain hand placements which may help keep people a bit more focused (maybe the bare attention required to keep fingers barely touching, for instance). However, don't make too much of this.  Ultimately, how you sit is a means to help facilitate your concentration and mindfulness, unless you believe that your suffering in life can be solved by how you hold your hands.