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Actually, it is clear from the chart that resistance goes up with diameter. The difficulty with the chart is that there are no "60" profile tires (or any with lower profile than that) to compare directly to the two 16" tires that were in the study. The questions, for which the study has no data to answer, are: (1) what would the data points be for 16" tires with profiles of 65, 70, 75, 80; and (2) where would the data points be located for 13", 14" and 15" tires that have a profile of 60? I think we can imagine how in very rough terms how those relationship might play out - that is an expectation or rough prediction.
As others have noted in this thread, there are other factors at play regarding total efficiency: (3) engine RPM at highway cruising speed (in which diameter functions opposite to the charts); and (4) the effect of tire weight both rotationally and linearly when the car accelerates (which reinforces the diameter relationships shown).
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