@ludek.. those groups are about marketing, not contests. When a customer does a search here on FAA the results are "weighted" by many factors as to whose images appear first. Previous sales is a major factor, but votes, visits, and group features also affect your search rating.
Also in a contest with hundreds or thousands of entries they are presented in the latest submissions first and the early submissions last. And when people go to vote most will look at the current standings first, and if you haven't voted for yourself they will not see your image. And again that is all about marketing. Winning a contest gets you no benefit in the search results.
bob