These are some lengthy and comprehensive considerations:
(This if the reader is not interested in the study or practice of the Gua, Flying Star, Bazi, then please give this article a miss.)
1. In order for the two Gua (or Kua) to be able to work together, they have to belong to the same denomination.
2. Please look at the chart, below:-
3. Please look at the Five Elements concept. Here, Flying Star Chart shares the same Lowest Common Denominator (L.C.M) as Ba Zi or 4 Pillars.
4. While Eight House or Eight Mansions or your Gua (Kua) although belonging to the Compass School has no L.C.M. with Flying Star Feng Shui.
4.1. Gua is like an orange. Flying Stars is an Apple. I can give you an Apple plus an orange. But I don’t have an Oran-Appl.
5. Thus Gua or Kua No. 3 is simply just that.
6. While Flying Star numbers are based on L.C.M.
6.1. Where #3 is strong Fire element. #5 = Strong Earth. And #2 = Weak Earth.
7. Bazi: Attached is a sample of an individual's Bazi report
7.1. See below. Extract of the above demo bazi report:
8. Bazi needs at least three major inputs:
Day of Birth
Month of Birth
Year of Birth
Optional = Hour of Birth.
9. With this input, it looks at the various interaction of the Heavenly Stem and Earthly branches. This interaction is based on the same L.C.M.
9.1. Contrast this to the rudimentary Gua (Kua). Although this is not the right way to compare both. But the Gua (Kua) needs only one's Year of Birth + Gender. Very Basic. Akin to kindergarten level of Feng Shui. Just nice to do it's job. But as mentioned previously no link whatsoever with the Five Elements Concept or L.C.M. at all, here.
10. And the final result: This person is a Strong Fire person or Five Elements Concept equivalent of #3.
11. As we can see, Flying Star Feng Shui uses the Five Elements Concept.
Plus Bazi also uses it.
12. For example, under Bazi:
Strong Earth Person is equivalent of Flying Star #5
Weak Earth Person is equivalent of Flying Star #2.
13. But wait a moment! There is still a difference between the two.
14. Bazi is based on an individual or "flesh and blood". While Flying Stars is based on a house's birth chart. An inanimate object.
15. I know what you are getting at. In this case, I use this person who has a Strong Fire element which is equivalent of #3 to boost the Flying Star right.
16. No it is not so simple.
17. In theory, you would need to learn how to embalm this individual and place this dead person at a SPOT. Does this sound logical. Or more of a horror movie?
18. The closest to your idea of a Gua (Kua) 3 looking like a #3 is based on the concept of Bazi Feng Shui.
Reference and extract of Case Study 26:-
==== Start of Extract ====
19. Case Study 26: How to Create good Feng Shui for a Home
1. Shapes and Forms and flow of q:. A straight path between the main entrance towards the windows at the living room. Is but one of the examples, here.
1.1. There is also the concern of the stove facing an open window in the kitchen.
1.2. Potential Sha Qi in the Master Bedroom if an extended wardrope is built as shown in the illustration.
2. Eight House: For example, Master bed-head direction is very suitable to Mr and Mrs. In addition, bed-head illustrations and study directions are optimal for both sons.
3. Flying Star Feng Shui: For example avoid Green in Bedroom 3.
4. Ba Zi Feng Shui: For example, the colours for Master bedroom and especially children's bedroom(s).
[Below] What if partition installed around the main door?
Ba Zi Feng Shui is abou the binding element of "partners" etc...
==== End of Extract ====
20. What is Ba Zi Feng Shui?
21. In the above example, Mr ABC is a Weak Wood Person. And Mrs DEF is a Strong Earth person.
22. Mr ABC's favourable elements are Water and Wood
23. Mrs DEF's fabourable elements are Metal, Wood and Water.
24. From above, both Mr ABC and DEF's Lowest Common Denominator are Wood and Water.
25. Thus, in areas where they "own" e.g. Master Bedroom, Living Room / Dining, it would be nice to consider "Wood and /or Water". BUT this is subjected to the house's Flying Stars.
26. For example, under Flying Star Feng Shui, Master bedroom has a combination of #9 = Fire element and #5 Bad Earth.
27. What is worse is that Fire further inflames or fuels #5 making it really bad. And can result in misfortune and sickness for those sleeping in this bedroom.
28. Fortunately, both Mr ABC and Mrs DEF's L.C.M. are that of Wood and Water.
29. As you can see, SW Master Bedroom; 1. Wood element and 2. Water element which harmonises both partners. We call it the BINDING element for the two can both benefit both partners. And at the same time both Wood and Water element can help to neutralize Flying Stars MS#9 with WS#5.
30. But this is not about embalming both partners in wax and permanently place them at that sector.
31. One method is the introduction of colours favourable to the two on the walls, curtains and bed-sheets.
32. Plus also avoiding Bright Yellow and Bright Red in this room.
33. The same principles apply to their two childern Child 1 and 2. Where both share the same L.C.M. of Metal and Water: What is the Flying Star numbers of their bedroom? Can Metal and Water element harmonize with the room's Flying Star numbers? In this example, fortunately both Bedrooms 2 and 3 (should they sleep together) indeed can apply Metal and Water element! Their binding element.
34. This whole concept is known as Bazi Feng Shui + Flying Star to harmonize a bedroom.
35. Sorry for the long winded write-up. I hope this helps.
36. Actually, under Flying Stars, it is a matter of looking at individual sectors and harmonizing that sector. Thus if the frontage of the home is at West, and there are unfavourable Flying Star numbers, the Mountain and Water star needs to be looked and either enhanced or cured.
37. Oddly, why should you want to enhance #3? As majority of the time #3 is not really one of the good numbers under Flying Star. As #3 individually represents Quarrels, conflicts and legal entanglements. LOL