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It will most definitely work for AVERAGE(). It should work for XIRR() also. We need SPECIFIC examples of where and how you are using these formulas.
Tell us what cell the AVERAGE() formula is in (if there really is one), and then tell us what cell the XIRR() formula is in, and show us what it looks like now.
If it (the XIRR() formula) is in K99, then if the values are in K and the dates are in column M, then the formula should look something like this:
=XIRR(INDIRECT("K2:K" & ROW()-1),INDIRECT("M2:M" & ROW()-1))
this would be the same as writing
=XIRR(K2:K98,M2:M98)