The book seems to suggest the opposite:
“A good general rule is that when an income statement or cash flow statement number is in the numerator of a ratio and a balance sheet number is in the denominator, then an average should be used for the denominator. It is generally not necessary to use averages when only balance sheet numbers are used in both the numerator and denominator because both are determined as of the same date.”
Institute, CFA. 2016 CFA Level I Volume 3 Financial Reporting and Analysis. CFA Institute, 07/2015. VitalBook file.
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