FlyingProxy will generate a separate cache when query strings are found. You can specify the queries separate by a new line or space and FlyingProxy will ignore that query (without rewriting the URL).
For example, by default https://example.com and https://example.com?ref=ad will serve different caches. You can add query strings like "ref" so that FlyingProxy will ignore that query string and deliver a cached page, for both URLs.
No need for regex in keywords. For example, "utm_" is enough for query strings like utm_source, utm_campaign, utm_medium etc.