I have not dug into the definition. Plain language reading, and I am good, personally, with RA or the PO Box's street address, in my case (where I am locally prohibited from using my home address). My DL has the same PO Box on it. My PO Box is my legal business location because of my local rules.
The above examples refer to "or" "business street address". I have two possibilities to use, RA or the street address provided by USPS for the PO Box. The first example even specifically mentions if no residential or business street address is available, so fincen has pondered this and offered at least a couple of valid alternatives. next of kin, nope, not doing that, but "another contact individual" looks good for using RA.
--
I do get it, some may think why bother. But, when you have had those with mental/moral issues contact you at your residence, you think differently. I am not the only one who lives in our home...