I use a lot of Ken Forkish recipes and I, too, find him very wasteful of flour in the starter recipes.
I just use proportionate amounts of the ingredients: in this case 360 is 36% of Ken’s levain of 1000 g total. For simplicity I round off to 40% all the ingredients: 40 g starter + 40 g WW + 160 bread flour + 160 g Water = 400 g. I have found that using 400 g levain instead of 360 g makes no difference in the final result. Happy baking!