Down with Canon flash metering in Av anyway.
Thank gosh my 1-DII does not have this feature. Keeps me away from Av.
I despise Av using Canon flash metering, disabled it on my 20D, and rarely do any Canon fill flash in Av because Canon E-TTL/II flash metering assumes all Av flash metered exposures want to ambient expose the background, having the camera default to too slow a sync speed.
Av flash algorithms are only useful from a tripod, or in bright outdoor light for modest fill (and not there much either).
Canon flash in M is better. M is pure. M is simple. M is the user in control.
M together with FEC and FEL is consistent results.
Boy am I ranting off on a tirade. Sorry. I shot an indoor flash event last night and am reminded of the dark art of Canon flash.
Jack