Operative term for the OP being in his situation long term gain for securities that are not approved by IRS for blended capital gains treatment.
A long time ago, I personally had an accountant "F" this up and I was audited. She said she could do it and I took her word for it. Subsequently when I got the dreaded IRS letter I got a few referrals from my futures broker for accountants who knew what the hell they were doing with futures contracts and offsets. On the advice of my new accountant who was really well versed with futures offsets - I simply wrote a check to the IRS for what they were asking for. Point being, I really didn't want the IRS combing through years of tax returns during the course of a contested hearing.
https://greentradertax.com/trading-futures-other-section-1256-contracts-has-tax-advantages/
Completely agree @bone
Too many if/then branches in the tax code for trading, beyond the (misunderstood) "basics" often discussed here in ET, like TTS, MTM election, and deducting a home office.
Consult a trading tax professional!