This information likely exists one or more places on the forum already. Since I couldn't easily find it, I'm sure most of the rest of you can't easily find it - so I'll write it again in one place.
Working on the simple, single guidance that "closer is stronger," I encourage the use of a simple trick Garth Allen recommended for dealing with orbs. Here is how I wrote about it in the current draft of the CSA chapter on aspects:
The most important message from this is that orbs are fluid. There is nothing absolute about the cut-off points. They are a convenient way to organize the gradually increasing and decreasing strength of aspects and angularities. The second point to understand is that boundaries of 3°, 6°, and 9° are reasonable cut-offs especially for beginners - nothing complicated, easy to remember, and work fine enough. The third point (not actually stated above) is that we can refine these boundaries with more precise measurement to calculate more narrowly when steeper drop-offs occur. A final point is that, while such boundary refinement is indeed useful, it's not a huge deal - aspect strength is fluid and gradual. No matter where you set the Class boundaries for yourself, you need make a big deal if an aspect is a little wider or a little closer....I strongly recommend a trick Garth Allen (Donald A. Bradley) suggested (1957) that has been basic to my practice for 50 years: Tabulate a chart’s aspects in three columns of close, wider, and widest orbs. Specifically, list major aspects for a given chart in three columns, those with orbs 0° to 3°, 3° to 6°, and 6° to 9°.
I call these orb ranges Class 1, Class 2, and Class 3, respectively... I also assign to the three classes standard “plain English” adjectives that astrologers often use without clear definition: When I call an aspect “close,” I mean it is Class 1. By “moderate” or “wider,” I mean Class 2. If I call it “wide,” I mean Class 3.
These groupings – and this way of thinking about aspect orbs – will make your astrological life much easier and more fruitful.
Within Class 1, we need one more distinction that astrologers (especially Sidereal astrologers) use frequently: Aspects within 1° of exact are called partile, which literally means “exact.” One could argue that “partile” should be used only for an aspect with 0°00' orb, but that is not how astrologers use it. “Partile,” by convention, means within 1° because aspects this close are mostly indistinguishable from those with a 0° orb. They are functionally exact.
Always notice partile aspects.
Therefore, we have four distinctions of aspect strength based on orb: exact (partile, within 1° of precise aspect), close (Class 1: within 3°), moderate or wider (Class 2: 3-6°), and wide (Class 3: 6-9°).
Partile aspects seem magical with their vivid strength. Class 1 aspects clearly stand out as important and essential, with a sharp drop-off in perceptible importance soon after 3°. At about 6°, the drop-off becomes steep.
This thread will layout the thinking behind the aspect and angularity scores in TMSA. I will break the discussion into four phases: (1) Trines, Squares, and Sextiles (2) Conjunctions & Oppositions (3) Major Angles, and (4) Minor Aspects & Angles.
