The data below show porosity for a well sorted scenario is independent of grain size (coarse vs fine, and very fine). However, the effective permeability actually reduces with smaller grain size (sorted or not).
If one reviews “Extremely Well Sorted“ for each grain size, they will see that the average porosity is about 0.424 (42.4%). Alternatively, for “Very Poorly Sorted”, the average porosity is 0.279 (27.9%).
These are unconsolidated sand examples.
References
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T. A. Blasingame “Reservoir Petrophysics: Introduction to Geology” , Texas A&M University, Course P663.
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Beard, D.C. and Weyl, P.K.: "Influence of Texture on Porosity and Permeability of Unconsolidated Sand," Bull., AAPG (1973) 57, 349-369.
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Morrow, N.M, Huppler, J.D., and Simmons III, A.B: "Porosity and Permeability of Unconsolidated, Upper Miocene Sands From Grain-Size Analysis," J. Sed. Pet. (1969) Vol. 39, No. 1, 312-321.