Yes, most CPAs have not encountered and the ambiguous safe harbor leaves many open questions.
I went with my financial advisor's (manage $4B of total asset, regional presence (Seattle main hub with other smaller west coast locations through buying out retiring advisory firms)) tax team. The long term heads of these tax depts handles fairly complex returns and usually have encountered Ponzi returns before. But these tax teams are only available for advisory clients.
Too small advisory firm (say few people) just enlist some local CPAs and they've often not seen it before (saw this case with one Ponzi victim, CPA had to communicate with IRS for many clarifications). Too huge firm (Schwab etc) have teams geographically distributed all over don't know how personal they get.
So I guess mid/largeish financial advisor firm's tax dept is best choice but only if you can access one. Most independent CPAs haven't seen Ponzi deductions before. Even ones that charge high rates (handles a lot of business returns)
