Never put quotes around tilde ~, so:

SSH_CONFIG_FILE=~/.ssh/config

if you have space(s); do

var=~/'foo bar/file'

Don't put quotes around tilde ~ if you expect the shell to expand it to your home, so:

SSH_CONFIG_FILE=~/.ssh/config

if you have space(s); do

var=~/'foo bar/file'

With the quotes on tilde, you prevent the shell to expand it to treat literally.