X2 peter great shot.
First off, no light in the world is going to be able to balance the ambient and compensate for the backlight in peters example. Perfect set up for a black and white as shown. Hopefully someone will close the doors, but either way, your flash is not going to be effective until she gets closer to you.
We always do dry runs 15 mins before the ceremony and i write the settings down and keep them handy for when the actual ceremony starts. Going to have to put it in spot when shes close enough and pick the areas where the flash will be effective. As she gets on top of you you will probably a stop overexposed but if your shoooting raw, simple fix in post.
Plus i chimp like a MOFo when the attendants are coming in so im pretty darn close when the bride starts to march. We always have shooters in different spots, so michelle, tell hubby to get the back half and you get the front half. For me, this is why i like my bracket and where ETTL comes in very handy with the head pointed directly at my bride, spot, probably plus 1- 11/3 and i think you nail the exposure when shes in the isle. never going to get the back door from where peters shot was taken.