the source for the % is the tax supplement provided by Fidelity which lists the official % for every fund, along with guidance how to apply it, see link below. (Fidelity should have directed you to this document rather than a tax specialist...).
SPAXX is not shown explicitly the have "various" for that fund you have to look up by name in this case, pls verify yourself but I also hold that fund and it should be 55.09%. Multiply the dividends from that fund by that percentage.
https://www.fidelity.com/bin-public/060_www_fidelity_com/documents/taxes/TY24GSESupplementalLetter.p...
