flush probabilities all in

[jack1234]

ok, simple one for all you math geniuses out there:

in holdem for advanced players Sklansky puts the chances of making a flush with suited hole cards around 6.5% (p.310). Now I'm a no limit player mostly (both tournament and cash), so this affects me mainly on all in situations where 5 cards are seen and raising all in, say the last 2 or 3, with Ax suited is sometimes necessitated due to massive blinds. My math always puts it higher than this (around 9.5%), so can someone lay it out for me please? i guess the complete sitution in mind is something like all in hu with A9s v AK, so breakdowns for flush would be useful as well as total probabilities.

cheers