.vim-bookmarks file always saved to edited file's directory instead of set location

[eggbean]

This is the relevant parts of my config:

if has('unix')
  let $VIM = "$HOME/.config/vim"
elseif has('win32')
  let $VIM = "$HOME/vimfiles"
endif

" vim-bookmarks
  let g:bookmark_sign = '⭕'
  let g:bookmark_save_per_working_dir = 0
  let g:bookmark_manage_per_buffer = 1
  let g:bookmark_auto_save_file = $VIM .'/vim-bookmarks'
  let g:bookmark_display_annotation = 1

No matter how I set g:bookmark_auto_save_file the .vim-bookmarks file always get saved in the same directory as the file with the bookmarks set. What am I doing wrong?