The suggested bib/big method suggest the shortest possible chain length. That's OK if you have the largest cog that the RD can handle, but if not, you would need to make the chain longer if the cassette was ever changed to one with a larger cog.

I still think it's smarter to use the little/little method where the chain is routed through the RD, as normal and made as long as possible without hanging loose or rubbing on the RD cage. This length will handle any cassette within the RD's wrap capacity without having to change the chain length.

If you deliberately exceed a RD's wrap capacity, then the big/big makes sense, but you should know that the chain will hang loose in the little ring and several of the smallest cogs.