When I use ido-find-file and press TAB I see the found filenames in a half windows size. Instead could it be compact, where can emtpy space removed?
Ex: 
minimal.el:
(ido-mode 1) (require 'consult) (require 'vertico) (vertico-mode) Please note that I am not able to use icicles due to consult does not properly work when I enable ivy-mode.
[UPDATE] The issue is reported to be fixed in Emacs 29 trunk.
I had this question myself and your post had stimulated me to finally research how to do it.
Here's the current solution (or rather a fix, because this behavior of the *Ido Completions* buffer looks like a bug to me) tested on Emacs 28.0.50:
(customize-set-variable 'display-buffer-alist '(("\\*Ido Completions\\*" (display-buffer-reuse-window display-buffer-at-bottom) (window-height . fit-window-to-buffer)))) Additionally, try out 'one-column output:
(setq completions-format 'one-column) ; or 'vertical / 'horizontal Documentation on display-buffer-alist.
P.S. I probably should have also mentioned that typing C-f (after C-x C-f calling ido-find-file) allows to fallback to non-ido find-file with the currently more standard completions buffer behavior. C-h f ido-magic-forward-char lists all C-f initiated "magic actions".
TAB shows all column format I believe than on the second TAB the list becomes wider and its heifght decreases. Would it be possible to show in same height if multiple TABs pressed? M-x prev RET). The end of the documentation C-h f fit-window-to-buffer might be addressing this issue. Though I didn't investigate thoroughly (yet). ido again to me. The list of completions gets "re-drawn" on the second TAB hit. There'e no such issue with emacs -Q completions. There's a chance I'll dig deeper (I already did but not enough to find the fix). I'll let you know if I have a solution/fix for that. icicles handles it well but I was not able to use it along with consult