May I use the average cost of both covered and uncovered mutual fund shares in reporting the gain, or must I compute the gain for each category?

The average cost of the covered shares is considerable higher that the uncovered shares.  The fund company split the proceeds of the transaction with the result that TurboTax computes the transaction as two sales, with a gain that is considerably higher than it would be if I simply used the average cost per share of all of the shares on the date of the transaction.