VideoStudio :: Use Picture In Picture (Grow And Cover Entire Background)

I used to use MediaStudio Pro to create picture in picture especially where the picture starts small and grows to cover the entire background video clip.

I looked for and found a video filter which I thought would allow me to do the same. However after viewing the 'help' for the filter and trying just about everything I could think of I cannot achieve what I want to do if start with a video clip and then have another video clip appear (very small) in one area of the background video and then slowly grow larger to eventually cover the background video clip.

I can make the picture in picture appear and grow larger but it covers the entire background video clip with black effectively covering it no matter what size my picture in picture is. I looked for a chroma key to cover the black out but could not find it.