2.1.916 Part 4 Section 188.8.131.52, AVERAGEIFS
a. The standard indicates the Average-range need not have the same size and shape as cell-range-1 through cell-range-n.
Office requires each cell-range-1 through cell-range-n to have the same size and shape as the average-range.
b. The standard states that argument cell-range-n is of type number, expression, reference, or text; while argument selection-criteria-n is of type reference or text.
In Office, argument cell-range-n can be of type reference and argument selection-criteria-n can be of type number, expression, reference, or text.