I'd like to second this suggestion. Left/Right/Center options would be great. Right now all images need to be drawn/designed to have the important elements on the left.
Maybe also adjust the opacity of the top UI bar, it took me a while to even realize the top part of the banner was under it. make the image show through a bit more, at the very least in the center where there are no buttons.
On at least one of the new-ish social media/artblog sites I've joined in the last five or six weeks- I do not mean to be deliberately vague, I've been doing enough adjustment to the lot of them along with the new UI here on FA that I cannot clearly remember which one it was now...bugged me enough I checked; it's on a Mastodon homepage banner- the only formatting example, or namely limit, I was given was the filesize ceiling.
There was no provided definition as to how high or wide it could or needed to be; I had to determine it by guessing, reposting and resizing it several times. Halfway through I just repeatedly resampled a blank white JPEG with unlocked aspect ratio and lossily resized it for the remainder of my attempts, before customizing it fully. The resulting dimensions were so much wider and worlds 'shorter' that I had no image to use as-is then crop to fit it that I liked, or that didn't need to be deformed to mutilation by modification of its aspect ratio, despite already having cropped the original down by more than inches.
I concur with DragonTalon; even if all a user wants to do is crop an image picked for their FA banner to half or a third of the total width, allowing them to stick it in the middle or flush to either edge of the banner-space would really be swell. Throw in a manual banner image 'stretch' toggle into the bargain if that's entirely fine with both FA and the user's preferences.
-2Paw.