It seems to me that using the ratio would be a reasonable way to estimate your incomes for 2021, and it's a lot simpler than forming a partnership. You could file your 2021 tax returns based on the ratio, then start keeping accurate detailed records for 2022 and later. This is just my personal opinion, and not official tax advice. Check with a tax professional and see what they think.
It would be better still, as I suggested earlier, to divide your investments into two separate accounts instead of having everything in one "giant pool."
The IRS is on the lookout for people who aren't properly reporting cryptocurrency transactions. If they question your tax return, you want to have simple clear records so that you can easily and convincingly show that you reported everything correctly.
