I18 question:

Conditions: 6-deck, H17, DAC, DAS, Surrender available

With the above conditions, my basic strategy chart says that on a player 11 v. dealer A I should double. However, the I18 says to double if the TC is +1 or greater. Is the I18 based on an S17 chart? Is there an ammendment for the H17 chart? Which should I follow. With a fresh shoe, if I am dealt an 11 and the dealer upcard is an A, what should I do?

Thanks!!