How to change the initial height of a UIRefreshControl?

Question

I have a UIRefreshControl in combination with a UITableView, and it works fine, except that I need a custom height when the update starts. I tried the following:

refreshControl.addTarget(self, action: "showRefreshing", forControlEvents: UIControlEvents.ValueChanged) func showRefreshing() { scrollView.setContentOffset(CGPointMake(0, -150), animated: true) } 

And it shows extra space during the update, however, it trembles. This is not at all smooth, and I wonder if I am missing a simple solution. I also tried changing the refreshControl height, but it will still use the defaul offset height. Any ideas?