Oh, I'm not sure how to get Mysidia working with Nginx at all, then. It uses .htaccess files to format how the urls are structured. You'll have to find some way of converting the .htaccess files that come with Mysidia into whatever Nginx uses, I guess?
(Unrelated, bc it may not help you, but with an .htaccess file you can also dynamically lower the php version used for a folder and all of its children... So even if you have a higher version installed, you can still force it to run an older version. I have more than just Mysidia on my domain and I need php7 for my other projects, but php 5.6 for Mysidia, ofc...)
PHP Code:
<FilesMatch "\.(php4|php5|php3|php2|php|phtml)$">
SetHandler application/x-lsphp56
</FilesMatch>