(defvar-local start-display-at-beginning-of-minibuffer nil)
(defun start-display-at-beginning-of-minibuffer (&rest args)
  (when (and start-display-at-beginning-of-minibuffer (minibufferp))
    (set-window-start-at-begin (point-min) (point))))
(defun set-window-start-at-begin (beg end)
  (when (< (+ beg 2) end)
    (set-window-start nil beg)
    (unless (pos-visible-in-window-p end nil t)
      (set-window-start-at-begin (+ beg (/ (- end beg) 2)) end))))
(add-hook 'window-scroll-functions #'start-display-at-beginning-of-minibuffer)
(add-hook 'post-command-hook #'start-display-at-beginning-of-minibuffer)

(setq icomplete-separator "\n")
(add-hook 'icomplete-minibuffer-setup-hook (lambda () (setq start-display-at-beginning-of-minibuffer t)))
(defun icomplete-vertical-reformat-completions (completions)
  (save-match-data
    (if (string-match "^\\((.*)\\|\\[.*\\]\\)?{\\(\\(?:.\\|\n\\)+\\)}" completions)
        (format "%s \n%s" (or (match-string 1 completions) "") (match-string 2 completions))
      completions)))
(advice-add 'icomplete-completions :filter-return #'icomplete-vertical-reformat-completions)