When Cadent Houses are stronger than Succedent ones?

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Bonatti and Lilly (possibly others) state that the 9th and 3rd houses are stronger than the 2nd and 8th. Bonatti specifically states that the 3rd is sometimes stronger than the 2nd and 8th but does not explicitly say when this is so. The logic for this view point is indeed solid because the 3rd and 9th aspect the Asc by sextile/trine, whereas the 2nd and 8th make no ptolemic aspects (like the 6th and 12th). I imagine that in matters pertaining to wealth a planet strong in the 2nd or 8th would be better than that same planet (as a significator of wealth or ruling the 2nd etc) being in the 3rd/9th. What I am mainly wondering is how this relates to delineating and predicting marriage/relationships.

In a friend's chart I am analyzing Venus is quite powerful in Libra, conjunct the pars spiritus, but is cadent in the 3rd (she is afflicted by a square to the Moon in Capricorn/6th, but planetary afflictions do not necessarily deny the possibility of fruition, even if they show that there is a likelihood that at some point the thing created will be destroyed or altered etc). Saturn rules the 7th and is in the 5th in Capricorn but square to Mars in Aries. The north node is in the 7th. The part of marriage is in Gemini and Mercury is cadent in Scorpio in the 3rd but is angular by whole sign houses. The native has been married once for about two years but that ended violently and with divorce (Saturn square Mars?). I need to get the respective dates from him for these events but am wondering if Venus can really be considered afflicted just because it is cadent in the 3rd, at least regarding marriage?

Also, along the same lines, looking at Billy Graham (available online) there seems to be very little info online about his marriage, but he appears to have been married stably for most of his adult life and I believe only had one wife. In his chart his ascendant lord, Mars, is conjunct his Moon in the 9th, both in Sag, but they are near the MC (though not by sign as it is in Cap). Venus is rather debilitated by being combust, in Scorpio and in the 8th. Saturn is the exalted lord of the 7th and is in the 5th in Leo, its detriment (however I am aware that within the Greek system detriment did not exist). So I am a bit confused on why he had such a stable and long lasting marriage unless Mars/Moon conjunction in the 9th is actually very powerful with regard to marriage (neither planet is really afflicted, and Jupiter is in Cancer in the 4th, though retrograde). I don't remember where the part of marriage falls at the moment.

Any thoughts on either chart (or both) or on the topic in general? This is a complex topic I realize and any help or research others have done would be greatly appreciated. Thanks in advance.