Question:

Which criteria do you apply when a planet is on the border between two nakshatras? Would I consider both Nakshatras? 

My Reply:

Whichever side of the border it is on, thats the nakshatra its “in” =).

The problem is that when it is really close to a border, slight variations in how we define and calculate things might change our opinion of which nakshatra it is in.

There is a principle called “bhava-sandhi” which can be applied here. The principle is that when a planet is close to a border it loses its effectiveness. Because it itself is not really “sure” which sign / nakshatra/ house (whatever border you are dealing with) it is really in.

So these planets on borders sort of “blur out” and get overtaken by other planets with more clearcut positions. In other words, you might consider the borderline planet to be in both nakshatras, but its probably better to consider it in neither nakshatra, and just blur it out. It would be conspicuous in interpretation because of its blurriness. It would be getting overrun and overtaken by things symbolized by more strongly situated planets.