Reading 29 of FRA. Page 427.

In a period of non-falling costs and inventory levels, the weighted average method of cost accounting will assign higher COS and lower ending inventory values compared to FIFO.

Given this, the claim is that the return on assets ratios would be lower under the weighted average because the incremental profit taken from the numerator (net income) will have a greater impact thatn the incremental decrease in the denominator (total assets).

To me, this makes sense only if NI always falls short of total assets, in which case the same absolute change in the numerator and denominator will amount to a smaller % change in the denominator, and thus the numerator will have the greater impact. I was wondering, though, is it ever the case for NI to be higher than Total Assets? If no, why not? If yes, then the CFAI statement is only a special (albeit common) case.