11 vs. Ace. Dealer checks for a blackjack and doesn't have it. Should you double if there's no blackjack. Should you double if you have 10 hoping to draw a 10 since the dealer can have no more than A9.
You only double 11 vs Ace if the dealer hits Soft 17, as far as 10 vs Ace...no way. Doubling down 11 is not about catching a 10. Its about the improved chances of catching a 10 ALONG WITH the chances of a dealer bust in case you miss your draw. 11 vs 10 is only 55 percent but part of that is because the dealer will bust 1 out of 4 times. As with an ace, the dealer will bust 1 out of 5 times still giving you that slight edge. But, when dealer stays on 17 then he will bust only 1 out of 7 which severly hurts your chances if you miss your face card.
But if you count, there is a basic strategy departure index for both of those doubles.
Standard Hi-Lo index for S17 says double 11 vs A at TC>=1, and double 10 vs 10 or A at TC >= +4.
When you think about it, with a deck rich in 10's, and you know the dealer doesn't have a 10 in the hole, doubling is safe. The probability of grabbing a 10 is a bit higher than normal and the dealer is not likely to get a 21 with an A showing and no 10 in the hole.