I have read few posts and watched few videos about how to use HSS in Godox/5D. So that I can try when I go to his place. So I should use flash delay when using RF? I don't remember exactly whether it was over exposed or underexposed when shooting in Av. We tried many settings, and I don't remember which one gave underexposed and which over exposed. My guess is underexposed, pretty dark or completely black. I was metering off of some decoration they setup for the ceremony. I think it's some kinda light coloured cloth and flower arrangements. Yeah, two 400w at full power bouncing off of the ceiling would be plenty of light and would be good too. Turning one light off wouldn't be good in this setup. The two weddings I attended last year and this one, they pick smaller aperture for flash light setup. I don't know why, but that's what they do. I still have those photos, I will check if there is any photo I shot where aperture is opened wider than f/10.