The Parāśarī system of “Vedic Astrology” has really useful rules for determining how a planet’s sign affects its dignity. The idea is that the host (owner of the sign) and the guest (occupant of the sign) have certain type of relationship, and that determines the dignity (Unless the planet is in its own sign, or, many say, in exaltation or debilitation).
The system defines all the relationships, which are easy to remember if you are learned in Vedic lore, and aren’t that hard to remember even if you don’t know anything about all that. I wrote a detailed post on this, called Determining Planetary Friendship and Enmity.
Now, the basic rules for friendship and enmity get modified based on the individual chart. Here is a pretty detailed description of how to do that: How to Read an Astrology Chart. The idea is that if the host is too far away from the guest (or too close, in the same sign), the relationship between the planets suffers; and if the host is a healthy distance, not too close and not too far, the relationship between the planets prospers.
Because this is a calculation of distance it is based on real space, not aṁśas (fragments, “harmonics,” “subcharts”) of space. If you’re not sure of the difference between the two: the “birth chart” is a map of the real spatial positions of the planets towards one another. The aṁśa charts are maps of aspectual relationships between them, they don’t indicate real spatial positions, but reveal subtleties of how those spatial positions relate to one another. Since the modification of friendship is a spatial consideration, calculate it from the birth chart, not from all the aṁśas.
The friendships between the planets is established by their spatial relationship (which the main chart reveals). Whatever relationships they have, they carry those into the subdivisions. For example if the Sun and Mars are a healthy distance, their relationship is improved, and this affects all the amśas. It doesn’t matter if, for example, in the navāṁśa they are too far apart.
— Vic DiCara
PS – I wrote this because a longtime blog-reader asked me to clarify a point I made in a previous post: “temporary planetary friendships are a spatial affair and therefore should be deduced only from the actual zodiac positions, not recalculated per each aṁśa”