I can't give you a definitive answer. But....
The actual D1 rule is:
15.5.3.2 (b)
"A fraction shall be created, with the amount received by the student-athlete (up to the value of a full grant-in-aid) as the numerator and the full grant-in-aid value for that student-athlete as the denominator based on the actual cost or average cost of a full grant for all students at that institution. ......" A straight forward reading of that rule leads one to the sort of calculation you have done.
The insructions on how to fill out the form that records this information is
here. Look at form 08-7 and scroll down to (g), which is the baseball instructions.
Here's the instructions:
"Indicate the total of each student-athlete’s cost for tuition and fees, room and board, and required course-related books, based on the actual cost or average cost of a full grant-in-aid for all students at your institution. [Note: If you use the average-cost method, do not combine in-state and out-of-state tuition to arrive at a single average cost for tuition. Calculate separate average educational costs for in-state and out-of-state students.]
Indicate a figure by dividing each student-athlete’s total countable aid by his or her cost for tuition and fees, room and board, and required course-related books, rounded off to two decimal places (e.g., .75). [Note: If you use the actual cost for tuition and fees, room and board, and books, the equivalent award is calculated by dividing the actual amount of institutional financial aid received by the student-athlete (numerator) by the actual value of a full grant-in-aid (denominator). If you use the average cost for tuition and fees, room and board, and books, the equivalent award is calculated by dividing the average amount of institutional financial aid received by the student-athlete (numerator) by the average value of a full grant-in-aid for all students at your institution (denominator).]"I don't understand what the second bolded phrase means. Still, I suspect that there actually is no advantage for in-state athletes by using the average cost method by itself. However, there may be an advantage if the state provides grants exempted from the equivalency calculation.