I managed to solve the problem, but I think there's something I don't understand. Basically, the problem presents only if I enable the option “latest results” in the section “Auto populate”. But since I'd like to use this option (not particularly important though), is there a method to always force a certain type of ordering (in my case: “name ascending”; there's only one post type, so I don't need relevance), indipendently of the options?
The question about “more results” in isotopic mode is still valid, though! I have a ton of posts and I'd like to reduce the limits in order to make the query faster, but in that case I'd need the option “more results”. If it's not possible, it's not a problem. Caching works very well.
P.S. If you still need to take a look: the credentials I provided are not valid anymore since I need to present the project today between 16:00 and 19:00 GMT+1, but I can provide new ones later.
As always, thank you very much for your support.