[Plugin: WP Super Cache] Caches / always

The default index page is loaded from cache *if* it is specified as
example.com regardless of the “Reject URI strings” settings. If referenced as example.com/index.php or example.com/index.html, caching can be prevented (which is what I need). But otherwise it cannot. If I try something like ‘/$’ or variations on that theme, then nothing gets cached. Any suggestions would be appreciated. Version 0.6.6. Its the cache component, not super-cache caching.