Windows phone button image size.

Hi,

I'm using Forms to build an application for iOS, Droid and WP. I need to have a button with an image on it, and adding a

<Button Image="back.png" x:Name="BackButton" />

produces the desired result. Except, in Windows Phone, the image is really tiny, like 1/4 of the size on Android or iOS. I have fought with getting the size adjusted for more than a day now, and have not been able to resolve the problem. That's why I am asking you.

Does anyone know how to set the size of an image in a button in Windows Phone?