Strange layout result on Android, correct result on iOS.

I'm using Forms with a xaml page that is defined as follows:

<pages:BasePage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:pages="clr-namespace:RapApp.Pages;assembly=RapApp"
             x:Class="RapApp.Pages.DocumentPage">
  <pages:BasePage.Content>
    <StackLayout x:Name="slContainer" Orientation="Vertical">
      <StackLayout x:Name="slSearch" />
      <StackLayout x:Name="slSearchResult" />
    </StackLayout>
  </pages:BasePage.Content>
</pages:BasePage>

In the 'slSearch ' there is a entry field and a button (with image). In the 'slSearchResult' there is a label (with 'Results:' as text) and below it a listview.
Both stacklayouts are filled in the code-behind. On iOS this results in a page with a entry field with a button next to it, height approximately the same as the entry field. Below it is a listview with the results (if any).
On Android (4.4) the search-box/button is at least 5 lines in height. Setting/Changing the HeightRequest seems to have no effect.
Any pointers to a solution would be appreciated.

regards