During the "comment" process, some made the argument that it should be 10% so it would be just like FATCA...
"Consistency is the hallmark of the unimaginative." Oscar Wilde
You can make it any lower percentage you like for any reason you like. All that does is potentially increase the amount of unverifiable information you obtain. For anyone who actually believes this information is valuable, the simplest thing to do is to require the names of the four largest owners. At a minimum, you would get one name. At a maximum, you would get four. (Some examiners will scratch their heads, wondering if you can do this.)
You would at least make dishonest people tell you a lie of substance rather than just allowing them to say: "Our biggest shareholder owns 8%" thus letting them off the hook for telling you anything at all.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.