Unfortunately, the RadAutoComplete control does not support such functionality where the dropdown containing the matching items appears on top of the control. If the behavior you are looking for is different, please share more information on your requirement.
Have a great rest of the week.
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal and vote to affect the priority of the items