Normally, when the dealer has a 1/13 chance of having an ace up, the -4.3% figure would be correct. But when the player's first card is not an ace AND the dealer has a one in SIX chance of getting an ace up, the disadvantage is MUCH greater than this.
I thought I had covered this by the 37% disadvantage in my calculation?
This thread has really got me thinking....
Thanks again for your word of warning Automatic Monkey.
Matt21