Is XIRR known to give a bad result when you have only two dates and values?

I have an investment that costs $29 on 1/29/2011 and generates $30.25 on
3/20/2011, so profit is $1.25. XIRR gives 36.1%, whereas a simple
interest calculation gives 31.5%. Simple interest was calculated as:

( $1.25 / $29 ) / (( End-Date - Start-Date ) / 365 )

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W