In the "Map Compare" feature, there is the option to select "Owned as found" and this adds a parameter "ownfound=on" to the URL. I've tried to add both "ownfound=on" and "ownfound=off" to the URL above, but it doesn't make a difference.
This means that this flag/option doesn't do anything in case of the Top Finders query and means owned caches are either always counted as found or never counted as found.
To check which it is, I made a bookmark list of 1 cache and found that the cache owner was NOT in the list. So unfortunately, the owner of the cache is considered not to have found the cache.
So, I'm afraid that adding the "Owned as found" flag to this query really is a new feature request that only a developer can help you with.