I've had good luck with off camera flash withe the flash on ETTL and the camera on manual.
As long as you don't exceed the flash sync shutter speed, you are OK.
The aperture is what the flash on ETTL "cares"about.
You could have used f11 at 1/160th or so on the camera and left the Canon flash on ETTL, as long as you have the off camera cord.
But flash meters are good or better.
It's good to know both ways so that you are ready if all you have is your camera and flash and no flash meter.
Practice, practice, and read that exif data so you know what you did!
