Flash/exposure compensation confusion

[f1charlie]

I was taking a photo last night with my D90 on aperture priority and SB600 on TTL, bouncing off the ceiling. Initial shot was slightly dark, so set +1 flash compensation on camera. Took shot - histogram was exactly the same. Set +1 on the flash (in addition to on camera) - same histogram. Set +1 exposure compensation - same result.
It was not until I opened up the aperture that I got a shift of the histogram to the right.
I could understand in the first two cases that if the flash was at max power then it couldn't give any more, but no change with exposure comp on the camera puzzles me.
Can anyone spot the flaw in my understanding?

 

[HoppyUK]

Not sure what you're doing with the exposure compensation and how that affects the settings in this case, but if the flash is maxed out the only way you'll get any more exposure is by dropping the f/number (as you did) or raising the ISO.

If the compensation drops the shutter speed (depending on what mode you're in) then that will make no difference to the flash exposure and, again depending on the circumstances, might make very little or zero difference to the ambient.

 

[f1charlie]

Ah, of course, if I was in aperture priority, you would expect exposure compensation to change shutter speed, so that would explain it. Thanks, I think it's becoming clearer!