Hello douglascrp,
for module evaluators you need to keep in mind that the request URL of an operation needs to somehow include the site short name in a way the site module evaluator can process and check your filter settings against. For instances, when you call the form web script to render a form, the URL of that web script does not include the identifier for the site and thus the site module evaluator has no idea what site is the current context.
Furthermore, since the site module evaluator does not know which site is the current context, it assumes "global context" and you have not set the "applyForNonSites" parameter to "false" - by default it is evaluated as "true" which means that your configuration is used every time the site context can not be determined.
TL;DR - The evaluator behaves correctly in your case. You have a small configuration error to restrict the evaluator only to sites. When loading forms there is never any info about the site context so you can't configure forms specific for a site.
The only chance you'd have is when you add your own, site-aware form web script and change all calls to the out-of-the-box form web script to use your site-aware form web script.
Regards
Axel