On a cropped sensor, like the 7D with 18 megapixels and an ultra wide lens, you really don't need to go past F11-13, F16 would be my absolute max on a cropped sensor. Remember, the smaller the sensor the greater the natural depth of field. F20-22 is for something like a full framer, and even then only needed when you are dealing with extremes of perspective and distance, like this below where the lens was probably less than 6 inches from the ice.
For a higher perspective like yours, if you place your center of focus properly I'm thinking a F7-9 range would have been sufficient, and would have kept the lens close to its peak, which I'm guessing is in the F5.6-7.1 range. It really is a tricky equation of distance to subjects, lens choice like wide to tele, capture format size from point and shoot to large format, and where you place your center of focus. As a rule of thumb though, at least with a cropped sensor, anything beyond F11-13 really starts to become a point of diminishing returns, where by any gain in depth of field due to smaller apertures is negated by a robbing of resolution due to diffraction. We could get a lot deeper into this, but for now that's kinda the Coles Notes version.