I did some digging through the different magit commands, and have found that there are quite a lot of them that essentially seem to do very similar things. For now, the following seems to cover all my current use cases, but I expect I will be adding more to the list in the future:

(fullframe projectile-vc magit-mode-quit-window)

Which is called when I activate magit from helm-projectile, and the rest are for magit-diff in various context (the names should be self-explanitory, and there are more - you can use M-x magit-diff- and look through all the available options/completions).

(fullframe magit-diff-staged magit-quit-window)
(fullframe magit-diff-unstaged magit-mode-quit-window)
(fullframe magit-diff magit-mode-quit-window)

I did some digging through the different magit commands, and have found that there are indeed a number of different commands for different contexts. For now, the following seems to cover all my current use cases, but I expect I will be adding more to the list in the future:

(fullframe projectile-vc magit-mode-quit-window)

Which is called when I activate magit from helm-projectile, and the rest are for magit-diff in various context (the names should be self-explanitory, and there are more - you can use M-x magit-diff- and look through all the available options/completions).

(fullframe magit-diff-staged magit-quit-window)
(fullframe magit-diff-unstaged magit-mode-quit-window)
(fullframe magit-diff magit-mode-quit-window)