Zoom into clip without altering scale (premiere pro)

I have tried to do this every way recommended, and its not working. I've tried nesting, generating black video, opacity masks, track matte key; nothing seems to work for me.

I have a standard video clip, 100% scale, no black bars.

There is another clip on the track above playing at the same time, but scaled down to 50% so they sit on top of each other. So you can see the corners/box of the video.

I want to zoom into a section on the scaled down video, but while fixing the 50% scale so i don't loose the desired effect of the two videos playing over the top of eachother.

Any solutions would be appreciated, and please try and be descriptive as I am no premiere pro expert.

Thanks