How would you explain a below than average Navamsa for a guru? I wouldn't say they don't have a sense of purpose, but can definitely say that marriage was not a path for a guru with a below than average D9. Perhaps Ju would be a more important planet in the D9 than Ve?
Using the techniques you teach in the concrete varga course.
You mean the principles from "Concrete Chart and Varga Analysis with Jaimini", right?
This is my guess: In this course, the navamsa is mostly used to analyze it for the average person, which means that it's centered around marriage and how anchored they are on their path. The entire course is about the concrete things in a person's life. Like you already mentioned, marriage might just not be concretely supported in their life because their focus is on spirituality. Hence the factors you mentioned (DK, Ve, 9th, 5th, etc.) being below average.
Below average might also mean that they are not particulary anchored on their path or dissatisfied and that's the reason they're turning to spirituality in the first place, because they are looking for an anchor.
Have you compared those factors to the Upadesa Sutra factors for "Dharma from the Svamsa's 9th" from the Jaimini I class? I wonder how they compare and whether the chart in question also has troubled dharma factors.
Its best to start the analysis of the navamsa, espeically in Gurus, from the Jaimini point of view and remember also the yoga of the first and 5th lords or the AK and PK to be joined or aspected and if debilitated or exalted the yoga gets stronger, so sometimes even a DB planet in navamsa will be helpful. And of course, there will be factors that deny marriage.
y es, the lagna and 5th or ak and pk joined or aspected in rasi, drekkana or navamsa is a raja yoga. use the lagna and 5th lords from the rasi only. if they are ex or db the yoga is more powerful.
I taught it somewhere, but dont remember where.