you got it, your example looks correct... as for the minimum state % I'm not familiar with anything specific to Illinois but CA, CT and NY are usually referenced for needing minimum 50% to qualify. See these supplemental tax info letters from Fidelity and Vanguard which both talk about the calculation so you have something more official to refer to, and have the reference to specific requirements for those states. Unfortunately Merrill doesn't do a nice letter like this as they don't own the funds...
https://www.fidelity.com/bin-public/060_www_fidelity_com/documents/taxes/TY24GSESupplementalLetter.p...
https://investor.vanguard.com/content/dam/retail/publicsite/en/documents/taxes/USGO_012025.pdf
