If full moon tithi spans two nakshatras which do we focus on?

Sometimes the full moon tithi will span two nakshatras, when it does which one do we use to determine what events, full growth and success possibilities the energy of that month is giving birth to and the lord of the month?

It seems like in Kala, that if a full moon occupies two nakshatras the traditional nakshatra is given precedence and only when the full moon is completely in another nakshatra does the lord and nakshatra of the month change. This is true even if the full moon spends most of its time in the non-traditional nakshatra.  Is there a particular reasoning behind this attribution?