Well, what I can personally offer is to answer questions I understand well. I don't mind writing a detailed reply, but doing additional research beyond a google search or two is more than I have time for. My answer above is an outline of what I would do, and actually what I do when I'm working with WALS. So aside from doing that for you, that's the most I can help.
If you have a simpler question or a different question, feel free to ask it, and if I know the answer I'll be happy to reply. Reading what you wrote above, I'm not sure about this one. At best I could spend more time reading the WALS page and then offer some guesses but that wouldn't be as valuable as you spending some time thoroughly investigating it.
(A little less on topic, I will add that the goal of this forum is to bring people together who have different areas of expertise so that hopefully one of them can easily answer your question. I'm working on trying to get the forum to grow, although I realize that right now there might not be anyone else here who works with WALS much. So in theory you shouldn't be addressing your questions to me specifically, and I would hope that someone [maybe me] can answer whatever questions you have. Maybe soon!)
As for this type of question, it would be a lot easier for me to answer something like "What is symmetrical case?" But what you are asking about is the data for specific languages, and that requires a lot more detail. And usually for a question like that I'd go to WALS or a similar source, maybe Wikipedia, for a definition, or write one from my own knowledge, and leave it at that. Figuring out why a certain language is coded a certain way in WALS can take some time even if you know the topic fairly well. So what's why I'm suggesting you do the background research for it. WALS is great for
at least a "quick and dirty" answer to general questions, and it provides a strong starting point for more specific questions but getting involved to that level can take a lot of work. The best thing about it may be that all of the sources are cited so you can find more information as needed.
Anyway, I'm not complaining at you. I'd be happy to answer if it was easy for me to do so.
Although I'd also encourage you to dig in with the background research

(Sometimes I find myself spending a lot of time investigating one very small detail for papers that I'm writing when that detail isn't really central at all to my work, but I just don't want to misrepresent it. Sometimes this is fun, other times very tedious. Normal part of research though.)