Thanks @dmertz
You're right, TurboTax's worksheet isn't comprehensible or up-to-date.
I'll contrast that with your answer, which satisfies on both accounts! Cheers to you.
In the future, I'll ignore the TurboTax worksheet, and use this nifty one that I found from Fidelity.
https://www.fidelity.com/bin-public/060_www_fidelity_com/documents/customer-service/401k-self-employ...
