SNI sites behave the same like non ssl namebased vhosts. So if no domain matches the site(s), the first site in alphabetical order is shown that uses the same IP address. If you want a specific site to be shown first, just change the domain name.
Example the site example.com shall be shown first:
1) Change the domain name example.com in the site settings to 000example.com
2) Add example.com as aliasdomain to the site 000example.com