I would take a photo. Look at the results. Adjust exposure and shoot again. Look at results. Get frustrated because everything was wrong. It turns out that in flash photography Aperture and Shutter speed work differently when you're using Flash. OH OK. Ultimately it is logical but hardly intuitive.
Suffice that aperture controls the exposure of the flash light only and shutter speed controls ambient light exposure. Considering that flash light is many times more powerful than ambient light when you're using a flash, it follows that aperture opening wider will have far more affect on the influx of flash light immediately upon shutter release and lingering shutter will affect ambient light because flash light is non-persistent.
See, logical. I was thinking of the flash light as ambient light, persisting and constant which is entirely false with flash. Flash does, by definition, flash.
I felt dumb last night when I realized that elbow deep in four books on flash photography. I think I even slapped my head a little.
Which killed those brain cells.
And I forgot everything.
What? What happened? Who are you? Get off my lawn!